With the GOP coalescing behind Mitt Romney, the Republican frontrunner is turning his attention away from the bitter GOP primary and toward the general election fight against President Obama. One of the most important decisions Romney would face as the Republican nominee is his choice of running mate, which is considered the first test of a candidate's presidential mettle. If Romney chooses wisely, his campaign should get a boost. If he blows it, his odds of winning could sink. Who should Romney have by his side? Here are six early favorites:

1. Rep. Paul Ryan (R-Wis.)
"Mitt Romney and Paul Ryan have something of a 'bromance' going," says CNN. Ryan, the House Budget Committee chairman, is a hero to fiscal conservatives, so when the Wisconsin representative endorsed Romney, he helped seal the presidential frontrunner's Tuesday victory in the crucial swing state. After his win, Romney asked Ryan to introduce him at his victory celebration, and Ryan delivered "just the sort of attack-dog rhetoric" against Obama that Romney will expect from a running mate, says Chris Cillizza at The Washington Post

2. Sen. Marco Rubio (R-Fla.)
"The widespread speculation has been that Rubio is the leading contender," says The Washington Post. "He's popular with the Tea Party," so he could help Romney win over the "anybody but Mitt" crowd. And his Cuban-American heritage could help with Latino voters. "But the 40-year-old first-term senator is untested on a national stage, something one Romney supporter said 'absolutely' gives the Romney team pause." Not only that, but Rubio has joined a growing list of GOP rising stars — including South Carolina Gov. Nikki Hailey, Minnesota Gov. Tim Pawlenty, and New Mexico Gov. Susana Martinez — who say they're not interested

3. Gov. Chris Christie (R-N.J.)
Romney, a moderate former governor of blue-state Massachusetts, is an "entirely conventional Republican," says Ted Van Dyk at Crosscut, so he's "not someone who will make a risky or dramatic choice." That means, for example, that Romney's not going to do something like pick his biggest primary opponent, Rick Santorum, whose "social-issue baggage" would be a liability come November. "Romney's obvious alternatives include New Jersey Gov. Chris Christie, whose political appeal parallels [Vice President Joe] Biden's" — he's popular, and a "loyal and active defender" of his team's policies. Two other similarly qualified possibilities: Louisiana Gov. Bobby Jindal and Sen. John Thune of South Dakota.

4. Rep. Allen West (R-Fla.)
Sen. John McCain went "rogue" in 2008 when he picked Sarah Palin. Would Romney forget about playing it safe and do the same? Sarah Palin thinks he should, says Mackenzie Weinger at Politico. Palin told Fox News this week that the GOP nominee shouldn't play it "safe." At the top of her list of suggestions? Rep. Allen West of Florida, a Tea Party firebrand who Palin says would be a strong ally in a what will likely be a bruising fight. "I love that he has that military experience... He understands the Constitution. He understands our national foreign policy issues that must be addressed." 

5. Gov. Bob McDonnell (R-Va.)
6. Sen. Rob Portman (R-Ohio)
There are a lot of names being bandied about, says Doug Mataconis at Outside the Beltway, but "at the end of the day, it seems like the likely VP running mates are the same two people that have been mentioned for most of the past year, Ohio Sen. Rob Portman and Virginia Gov. Bob McDonnell." Both "have a deep well of experience and ties to the conservative wing of the GOP," and both come from states that will be critical in November. Still, both men come with negatives — Portman was George W. Bush's budget director, "an unfortunate reminder" of GOP mistakes, and McDonnell's social conservatism and his state's controversial recent abortion legislation might not help close the gender gap.