As a GM of both MnM and HERO, I would have to say MnM is probably better out of the box for supers as much as I love HERO. Both games can do supers well and comes down to Player and GM preference. I know a number of ex-HERO players who left the crunchy world of HERO for MnM and not looked back. At times I do have issues with HERO but have been playing or running it since '82 (in the form of Champions) that I'll overlook it's issues and I'm blinded by her beautyThe problem with comparing the two is the premise behind the books are different. MnM is fundamentally a core book of rules centered around the supers genre (like Champions started out back in ~1980). HERO on the other hand are a set of rules to let you build the game that you want to run (toolkitting). Now MnM is starting to look like HERO did back in the late 80's early 90's where a number of people were starting to use MnM for other genres and styles of campaigns as can be seen in the supplements Warlocks and Warriors and Manga and Mecha. When 4th edition of Champions/HERO came out, that was the split between using the rules as a toolkit to build campaigns (HERO System) and different books to support genre (e.g. Champions Genre book). Although to be fair both rules and genre were put together as one book called the "Big Blue Book" Champions book and other genres had their own book like FantasyHERO and StarHERO. By 5th edition the split was total. The core books only had a small chapter on different genres and there was no assumption in the rules that a specific genre was being used.Ultimately I voted for MnM assuming you wanted supers right out of the box. HERO can do that but you have to put more of the work into it if you don't want to spend money for supplements. There is a significant amount of conversion material on the web though that can give you an idea of how to build various comic and other media characters as evidenced by Surbrook's website full of HERO writeups. Also you can visit the HERO forums which is very active and helpful. You can read over how everyone tries to come up with how to implement a particular power or get help if you are having problems coming up with a power build. You can also find additional resources there as well.Considering that you had the 5e HERO book and didn't spend the time to try to use it, you may be better off using MnM. If you want to try HERO 6e though without the large by in, I would highly recommend getting the HERO System Basic Rulebook. The Basic book has most of the powers and rules you'll need to do good job of running a supers game. It's only $20 and you can do ~90% of what the two base books do (Book 1: character creation and Book 2: Combat and Adventuring).From a mechanical side MnM uses a d20 rollover. The difference rolled over determines the degree of effect and the same mechanic is used for skills.HERO uses d6's. Skill/Attack resolution in HERO is 3d6 roll under some target number with power effects rolling a number of d6's usually. For example a typical energy blast (Human Torch doing a Fire Blas) may do 10d6. The total is added to determine the STUN done. Using the same dice BODY is determined by adding +0 for 1's, +1 for 2-5, and +2 for 6's. This is the problem that a number of the ex-HERO players have is the dual damage calculation. Yes it takes extra time, but once you get used to it I don't find that it's that much and there's ways to batch it so it's counted faster (e.g. for a 10d6 you know you start with 10 and -1 for zero's and +1 for sixes).I've good and bad experiences with both games. Like any RPG it utimately comes down to GM and Players having fun and both games are rewarding in there own fashion. Currently I'm running HERO (Champions) and DnD 3.5 (Legacy of Fire AP) campaigns.Whatever game you choose I hope you and your players have fun.