Nominating someone as 'the best' is always tough. Because, what exactly does it mean anyway, what metrics do you take into account when determining what is 'the best'? Are we talking the most valuable player to the team, or just the raw ability compared to the rest of the team? Or the best and most productive of their position group amongst their peers throughout the league? What about irreplaceability?

MVP voters year in and year out mostly look at only one of those metrics, and it's about productivity. Never about dominance, or how much the team would be worse without them, or leadership. But, I don't think that is an accurate measure of who's the best player on a team as it usually skews it to offensive players who can put up gaudy stats like it's their job. I feel that it's important to take a more rounded approach when looking at players on a team and think about how they're interconnected, how much better are they than your average off-season free agent pickup, or how much would they detract from the team without their presence. Passing yards, sacks, and touchdowns don't really tell the whole story. But they're one way to determine value.

Lets take a look at what Pete Prisco wrote about his 100 'Top' players in the NFL and how he put 4 Bears players on that list.

31. Julius Peppers, DE, Chicago Bears: He had 11 ½ sacks and continued to be a good run player for one of the best defenses in the league.

38. Brandon Marshall, WR, Chicago Bears: He had 118 catches, third best in the league, and had 11 touchdowns in his first season with the Bears. The only knock is his yards-per-catch average, which was 12.8.

48. Henry Melton, DT, Chicago Bears: He is a penetrating up-the-field defender who plays with great quickness -- sometimes too much as he gets caught out of position in the run game.

70. Charles Tillman, CB, Chicago Bears: Even though he's getting up in the years, he's coming off one of his best seasons. He made a ton of big plays in 2012.

Now, just to be clear, I'm not here to quibble about their rankings as being some travesty, that the Bears are somehow more underappreciated now more than ever. But ask an honest question... who's the best player on the roster?

Julius Peppers is still one of the best all around defensive ends in the NFL. He's not the pure pass rusher that DeMarcus Ware, Jared Allen, Clay Matthews, Jason Pierre-Paul or Von Miller is, but there's very few with the sheer versatility and physical play that Peppers brings. His commitment to playing the run as a top pass rusher is second to none. If Peppers didn't play another down for the Bears, how hard would it be to replace him though? There's a lot of really strong, really good pass rushers in the league right now. The Bears could even still be effective at getting after the passer with the players on the roster if they added another potential pass rusher in someone like John Abraham or Dwight Freeney, even on a part time basis. Can't say it would be ideal (because how do you replace a bajillion time pro-bowler), but Peppers is, without question, one of the most talented players on the team, even though he's no longer one of the best or most dominant players at his position.

Brandon Marshall in Chicago has given me an opportunity to watch one of the best at his position. Unlike Peppers, Marshall is in that class of his own. Top 5 in his position, completely irreplaceable. But even with Brandon Marshall in 2012, the Bears didn't get that much better on offense. So you have to ask: how much does he actually mean to the team in wins? Suppose like we postulated with Peppers, if you replaced Brandon Marshall with Greg Jennings or Danny Amendola, how much worse off would the Bears be in 2013? Marshall, while dynamic, wasn't what held back the offense. That doesn't mean he's not going to have another monster year next year, where he's going to get 100+ catches, 1200 yards and 10 touchdowns and be a top 5 WR once again... But how does that translate to wins for the Bears? How much more can you ask out of a players who's pretty much giving everything he can at his position? You can't. Right now, Marshall is arguably the best player on the Bears by talent, with only Peppers giving him a run for his money.

Henry Melton is a different class of players here, and someone that I felt that Prisco was probably overvaluing on his list by quite a bit. That's not to say Melton isn't good, or even one of the best 4-3 penetrating defensive tackle, but there's just so many better players around him and in his position. His value, at 48, is way past what I think his contribution to the team even is. No no no, he's not Geno Atkins, Ndmukong Suh, or Gerald McCoy, but I think what Prisco saw in him was the potential he has for next year. Melton has two options in his game: either become more well rounded by improving his run defense like J.J. Watt, or become a Tommie Harris level interior pass rusher like Geno Atkins. In the NFC North you could make the claim that his overall value on the team is dramatically increased if he can penetrate the weak interior of the the Packers and Lions's offensive lines or disrupt the Vikings interior enough to shut off some of Adrian Peterson's gaps. Evaluating Melton with that lens would make him one of the most important players for the Bears in 2013. What his level of play would be in 2013 can dramatically dictate how effective the defense is against the rest of the NFC North, and that can mean the difference between taking a win from the Packers.

Charles Tillman is a specialist amongst cornerbacks. Disruptive, strong, big, tackling, and turnover creating not just while the ball is in the air. Not every system could use a player like Charles Tillman, but in 2013, he'll still feature a prominent role where he's asked to stop the guy he's covering and do so with aplomb. He's re-reaching his prime (shocking, I know), and that crafty-veteran savvy along with his still very real physical skills will keep him a solid, extremely effective cornerback for a few more years. But in 2013? Where is he? Fighting the big boys like A.J. Green, Calvin Johnson, Jordy Nelson, Dez Bryant, and Greg Jennings. Talking heads often times criticize teams for investing in cornerbacks, because they're not as important as safeties or defensive ends/outside linebackers on the defense. But, let it be known: Those talking heads are referring the Jets or Patriots. Not about every other team. Teams like San Francisco, Chicago, Tampa Bay, Seattle thrive with cornerbacks who are an integral part of transforming the team from just a 'good defense' to a 'great defense'. When you add great parts to a well settled system like San Francisco did with Nnamdi Asomugha, it's transformative and eminently dangerous. Charles Tillman does the same thing in Chicago.

The other players I'd make a legitimate case for being the best players on the Bears would be: Lance Briggs, Jay Cutler, and Jermon Bushrod...

Lance Briggs is always the silent killer on the Bears defense, truly never getting the respect he deserves in a system constantly overshadowed by Brian Urlacher, but always the 1b to Urlachers 1a, and this year he'll have the opportunity to shine unfettered by Urlacher's presence. I don't think you can respect his game enough. He's a big reason why the Bears have been so potent in their defenses on the outside. Briggs is fast and so good at attacking the holes, getting to the sideline and a solid tackler. In the modern league, there's very few players who do as much as he does, with the proficiency he does it.

Jay Cutler... well. Without Jay Cutler and with someone like Jason Campbell or Alex Smith or Kevin Kolb or Matt Flynn... what do you get? The Arizona Cardinals. If anything is as damning of evidence that Jay Cutler is a more important piece of the puzzle to the Bears than any other individual player, it's that the Bears have looked like a 3-13 team without Cutler. Detroit without Matt Stafford is still Calvin Johnson's team. Joe Flacco and Colin Kaepernick still have Ray Rice and Frank Gore respectively, and a good defense to boot. There's not a lot of players in the league that I feel are worth 4 wins to a team like Jay Cutler is. Drew Brees, Aaron Rodgers, Tom Brady, Adrian Peterson and Phillip Rivers are about as close as you could find to someone who means as much to the success of their team as Jay Cutler.

Jermon Bushrod. The franchise left tackle who hasn't played a single down for the Chicago Bears, but has singlehandedly changed the makeup of the offense by his very own presence, in a way similar to what Marshall did for the Bears in 2012, but on a much more important scale. The Bears line went from mediocre/bad to decently good with the addition one player. One player pretty much turned the tide of the offensive line being a hindrance the entire offense to being as good as the rest of the position groups on the offense. That says a lot about the value that the Bears place on Bushrod and the expectations riding on him and Aaron Kromer to protect Jay Cutler.

Overall, with all the qualifications that you could take into consideration, I feel Charles Tillman is the best player on the Bears, over all others. Without him, the Bears defense loses so much of it's edge, and we're not even talking about what he brings insofar as turnovers. We're talking about his ability to cover and shut down receivers. In 2012: Jordy Nelson, 6 for 84 with 0 TDs. Danny Amendola, 5 for 66 with 0 TDs. Calvin Johnson, 3 for 34 with 0 TDs. Andre Johnson, 4 for 35 with 0 TDs. Calvin Johnson, 5 for 72 with 0 TDs. WR's like them average 80 yards and a touchdown per game. Limiting them like Tillman has done adds so much value to the Bears when you can take away a strength of an opponent in a heavy passing league. When you factor in his willingness to tackle, his ability to force fumbles, he becomes the best player on the Chicago Bears.

Who do you think is the Best Player?