Story highlights Mitt Romney and New Gingrich traded attacks over immigration and border protection

Gingrich's attack on Romney over his financial investments ended up backfiring on him

Rick Santorum and Ron Paul tried to fight their way into the often two-man battle

Paul, with his quick wit and one-liners, was the crowd favorite Thursday night

Florida has been dubbed "ground zero" of the Republican presidential contest, so it should come as no surprise that candidates would throw tough punches in the last debate before the state's voters go to the polls.

Here are some of the most buzz-worthy moments from the Jacksonville showdown.

Toning it down

Thursday night's debate got started with a lengthy discussion about immigration and border protection.

Moderator Wolf Blitzer asked former House Speaker Newt Gingrich about an ad he ran -- and then pulled -- that described former Massachusetts Gov. Mitt Romney as the most anti-immigrant candidate. Gingrich said he's prepared to be "very tough and very bold" and he still thinks Romney is the most anti-immigrant of the four remaining candidates.

"The idea that I'm anti-immigrant is repulsive," Romney said, accusing Gingrich of using "over-the-top rhetoric that has characterized American politics too long."

Romney said he was glad Gingrich pulled the ad, adding, "I think you should apologize for it, and I think you should recognize that having differences of opinions on issues does not justify labeling people with highly charged epithets."

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That response from a fiery Romney got some of the loudest applause of the night.

Right back at ya

Gingrich tried to hit Romney again over his financial investments -- an attack that ended up backfiring on him.

"We discovered to our shock Gov. Romney owns shares of both Fannie Mae and Freddie Mac. Gov. Romney made a million dollars off of selling some of that," Gingrich said.

The line appeared to also shock some in the audience, who gasped at the claim. But Romney shot back, pointing out -- as he would throughout the night -- that his investments were handled by a blind trust and are in mutual funds and bonds, not stocks.

"And Mr. Speaker, I know that sounds like an enormous revelation, but have you checked your own investments? You also have investments through mutual funds that also invest in Fannie Mae and Freddie Mac," Romney said.

Touché.

Paul, Santorum want meat and potatoes

The crowd in Jacksonville wanted to hear about the issues, and former Sen. Rick Santorum and Texas Rep. Ron Paul tried to keep the focus on substance as they shouldered into what was often a two-man battle.

Asked if Romney and Gingrich should return any money made from Fannie and Freddie, Paul made no attempt to hide his indifference.

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"That subject really doesn't interest me a whole lot," Paul said.

Santorum also tried to cut off what he called "petty personal politics," asking, "Can we set aside that Newt was a member of Congress and used the skills that he developed as a member of Congress to go out and advise companies ... and that Mitt Romney is a wealthy guy because he worked hard?"

A roaring crowd welcomed the suggestion.

Paul has jokes

The Texas congressman might not be No. 1 in the polls, but when it comes to one-liners, he was the crowd favorite.

Asked where he stands on Gingrich's proposal to put a permanent base on the moon, Paul said, "Well, I don't think we should go to the moon. I think we maybe should send some politicians up there."

Paul also had the crowd cheering in response to a question about releasing his medical records.

Paul, who at 76 would be the oldest president of the United States if elected, said he is willing to make his medical records public, noting that "it's about one page, if even that long."

"I'm willing to challenge any of these gentlemen up here to a 25-mile bike ride any time of the day in the heat of Texas," he continued, "But, you know, there are laws against age discrimination, so if you push this too much, you better be careful."

Paul also turned a more serious topic -- U.S. trade and travel policies with Cuba -- into a humorous moment.

"Imagine you're in the Oval Office, you speak to Raul Castro. What would you say to him?" Blitzer asked.

"Well, I'd ask him what he called about, you know?" he responded.

In a debate marked by some intense moments, Paul's wit was appreciated by audience members.

What was you favorite moment of the debate? Weigh in below.