If only there was a simple way to compare their strengths and weaknesses...
Who's got the most campaign money? Who really electrifies a crowd? What is their Achilles heel?
All your questions are answered - on a candidate card, so you can test the powers of one against the other.
Trump has been tops for so long it's hard to remember what the Republican race was like before he emerged on the scene. The New Yorker has thumbed his nose at political convention, embraced controversial positions that would be radioactive for other candidates, dominated the headlines and kept his opponents perpetually off balance.
He appeals to disaffected Republicans across the board, whether they're evangelicals, grassroots Tea Party supporters or even moderates. It's been an incredible run - but can it hold up once voting starts? He's shown a thin skin and flashes of a temper that, if repeatedly provoked, could eventually prove his undoing.
Dismissed when he launched his campaign last March, Cruz has cruised to the top of the Republican pack thanks to a gift for rhetoric and a campaign strategy that has taken advantage of the anti-establishment mood among conservatives. He's formed a seemingly unlikely coalition of religious voters, libertarians and Tea Party activists.
To win, however, he'll have to fend off attacks from Republican colleagues who overwhelmingly dislike what they see as his me-first attitude.
Rubio looks like a winner. He's charismatic, he has a compelling story as a child of Cuban immigrants, he's generally well-liked by the Republican establishment, and he's run a largely error-free campaign. That probably explains why every candidate not running as an outsider has done everything they can to tear him down.
Rubio is distrusted by grassroots conservatives, however, for his leadership on the 2013 immigration reform efforts that have since become politically toxic. He's the second choice of many Republicans, but he'll have to find an opportunity to break away from his mainstream competitors or risk falling too far behind someone like Trump or Cruz.
Many Republicans practically begged Christie to run against Mitt Romney for the Republican nomination in 2012. That was before he became mired in scandal in New Jersey and turned many conservatives against him for seeming to be too supportive of Barack Obama.
In 2016 his brash, straight-talking New Jersey style has been one-upped by Trump and his limited resources have forced him to set up camp in New Hampshire in the hope that a win there will surge him into national viability.
He has solid political-street-fighting abilities, however, so in a crowded, rough-and-tumble battle for the mainstream Republican vote, he could still claw his way to the top.
Bush once was the man to beat. His huge campaign war chest and solid support within the party deterred Mitt Romney from entering the race and hampered other establishment candidates. He's proven to be a paper tiger, however.
After nearly a decade out of public office, his political instincts seem dulled. He's constantly fumbled with his words, leaving him overmatched against more skilled debaters. His depth of knowledge on policy issues has been no match for Trump's headline-grabbing pronouncements.
His famous last name seems a detriment in the Republican electorate's anti-establishment mood, and moderate positions on immigration and education reform have hurt him with the conservative rank-and-file.
He's burning through money, but he still has plenty of resources. His best hope now is a long, drawn-out nomination fight where he's one of the last few left standing.
Kasich entered the Republican race because he perceived the nominal front-runner, Jeb Bush, to be weaker than at first thought. The Ohio governor has turned out to be only a slightly less flawed version of the man he sought to supplant for the mainstream Republican vote, however.
Like Bush, he isn't trusted by grassroots Republican voters who dislike his perceived heresy on healthcare reform in his state. His sometimes-dour demeanour has hurt him during the high-profile debates, where he's struggled to get attention.
If he has a shot, it's in New Hampshire, where he's in a tight battle with Bush and other more traditional politicians for second place behind Trump.
At one point last year the Carson-Trump outsider duo dominated the race for the Republican nomination. While Trump continues to flourish, Carson has fallen on hard times, however. His soft-spoken personality now seems ill-fit for a campaign that, after the Paris and San Bernardino attacks, increasingly rewards bellicose rhetoric.
He's also been repeatedly criticised for lacking a command of the issues. While he's posted eye-popping fundraising numbers, his campaign operation has been accused of mismanaged finances and beset by staff turnover.
He has a loyal cadre of supporters who believe in his intellect and adore his story of successfully overcoming childhood poverty, but at this point they're all that he has left. He'll need a surprise showing in Iowa, where evangelicals once backed him, to turn things around.
Fiorina turned out to be the surprise of the early Republican debate season, dominating the first undercard debate and emerging as one of the clear winners of the second, prime-time debate. She's never managed to capitalise on that surge of interest, however.
Thanks in no small part to the Trump phenomenon, she disappeared from the headlines for long stretches at a time. Her background as a high-tech corporate executive has left her with no natural political base, and she has seen a steady decline of her poll numbers.
She's once again off the main debate stage - perhaps for good - leaving her scant opportunity to recapture that earlier magic. With limited campaign resources, she's been unable to build much of a ground game in the key states of Iowa and New Hampshire.
Paul was once labelled "the most interesting man in politics" and predicted to be a force in the Republican nomination fight. If he could put a more mainstream spin on the libertarian appeal of the past presidential campaigns of his father, Ron Paul, he could carve out enough support to come out on top in a crowded field.
Instead, he seems to have alienated the libertarians, while the Republican establishment suspects his views on national security and foreign policy are too dovish. His fundraising has underwhelmed, as he's failed to attract deep-pocketed donors and the grassroots contributions pale compared to his father's money-generating machine.
He's shown a thin skin when facing hostile media questioning, and while he's offered a contrasting viewpoint during the Republican debates, there just don't seem to be enough Republican primary voters out there who agree with him.
It seems hard to believe, but Santorum won the Iowa caucuses four years ago and amassed enough votes to finish second behind Mitt Romney for the Republican nomination. At the time his combination of evangelical support and working-class sensibilities were an appealing contrast to Romney's corporate gloss for many Republican voters.
This time around, there are simply too many other candidates with more money, more experience and more personality for Santorum to compete.
He's staking everything on another surprise showing in Iowa, but there are no indications that lightning will strike twice.
If Santorum is yesterday's candidate, then Huckabee is the candidate from the day before yesterday. He was the surprise winner of the Iowa caucuses in 2008, running as a good-humoured conservative with a folksy charm.
The former Arkansas governor then eschewed a continued political career for a run as a radio and television talk show host, passing on a chance to run as a favourite in 2012. Now, like Santorum, he's been outmanoeuvred and outgunned by a host of new faces, and he's never been able to gain traction on his old terrain in Iowa or elsewhere.
He's still got the gift for gab, but his jokes are now on display in the undercard debates and his time appears to be running out.
Eleven Republican candidates are doing battle for the White House and after months of campaigning their first electoral test, in Iowa, is just days away.