Most early head-to-head polls show John McCain and Barack Obama as the strongest candidates in a general election, a reflection of their slight edge over their primary opponents among independents, who make up at least a third of the electorate and often determine the outcome.

But “electability voters” need more than polls. With the stipulation that 10 months is an eon in politics, let’s make some educated guesses about the pros and cons of how each of the plausible candidates would do in the Big Show.

Warning: these assessments could be thrown off by unexpected developments, the entrance of a third-party candidate or the particular dynamics of various matchups of Republican and Democratic nominees. Plus, I could just be flat wrong.

The candidates in both parties are listed from least to most electable:

REPUBLICANS

Fred Thompson

Pro If he somehow got the nomination his down-home style would wear well nationally.

Con He’s a lackadaisical campaigner who generates little excitement, even among Republicans.

Bottom Line Canceled for the fall season. He’s Bob Dole without the sense of humor or deep experience.

Rudy Giuliani

Pro His moderate positions on issues and his 9/11 calling card would sit well with pro-choice swing-state independents worried about national security.

Con Rudy’s strong support for the Iraq war, promise to appoint anti-abortion justices in the mold of Clarence Thomas and Antonin Scalia to the Supreme Court, and backing of President Bush’s veto of the children’s health bill would negate his appeal to moderates in Blue states. And his profiteering off 9/11 and ugly personal life make him a fat target. Expect New York City firefighters to appear in ads trashing him, which would undermine his message.

Bottom Line Unless the United States is attacked again by terrorists close to the election, a risky choice for Republicans.

Mitt Romney

Pro The former Massachusetts governor, a proven vote-getter in a liberal state, looks and sounds presidential. His record of success in business would play well in debates, and his personal fortune could help close the Democrats’ spending advantage before post-convention public financing kicks in.

Con He’s got no common touch. He’s easy prey as a flip-flopper. And as much as a quarter of the electorate—mostly Republicans whom he must have—say they could never vote for a Mormon, which is more than three times as many as those who say the same thing about a female or African-American candidate.

Bottom Line If anti-Mormon Republicans stay home, it’s hard to see how he makes it in November.

Mike Huckabee

Pro Likable, silver-tongued, strong on middle-class economic issues that appeal to Reagan Democrats, speaks “American” with a series of amusing stories and folksy metaphors that will not seem threatening to the nonreligious when they get to know him. His background as a Southern Baptist minister could help him tap churchgoers who don’t usually vote.

Con Gaffes on foreign policy already dogging him, and his Arkansas ethics problems may undercut his theocon image. With Rush Limbaugh and Republican regulars trashing him, might not hold the secular pro-business part of the GOP base. Could lose nonchurchgoers who usually vote.

Bottom Line A big risk, but he’s got potential appeal to Reagan Democrats, which might be the only way for the GOP to hold the White House.

John McCain

Pro Appealing, moderate, experienced, especially on foreign policy and national security, and his maverick streak and war hero status have long made him a favorite of independents and even some Democrats. Might put Blue states in play.

Con At 71, he’d be the oldest president, and looks it. In a “change election” he would seem like a figure from the past, especially on domestic issues. GOP base would be lukewarm about its nominee.

Bottom Line If there’s major news from abroad in 2008, he’s the GOP’s best shot. If not, he’s not.

DEMOCRATS

Chris Dodd

Pro Seasoned, accomplished, presidential.

Con If he can’t light fires in Iowa or New Hampshire, he lacks the mojo to win.

Bottom Line Highly electable, but not gonna get the chance.

Bill Richardson

Pro Experienced as a governor, congressman, cabinet secretary, diplomat. Could wake the sleeping giant of American politics: the Hispanic vote.

Con Not connecting, and would be vulnerable in debates.

Bottom Line Probably won’t be veep, either.

Joe Biden

Pro Strong foreign-policy chops in a churning world. Buoyant campaigner. More likable northeast Catholic than John Kerry, which might be all that’s needed.

Con High risk of gaffes, plus an energy-killing long-windedness.

Bottom Line Plenty electable, but after 35 years in the Senate he would have a hard time carrying the Democrats’ message of change.

John Edwards

Pro Dynamic, disciplined campaigner with general election experience. Taps into economic anxiety. Regional advantage, considering that the only two Democrats elected president in nearly half a century were both white Southerners.

Con Choked in ‘04 veep debate with Dick Cheney. A weak record, and pro-business Senate votes make him seem like a flip-flopper. Hard-edged populist message has always been a general-election loser, but if he tacks away from it, he’ll get hammered. Trial-lawyer style has shown little appeal among indies.

Bottom Line Looks safer, but at least as big a risk in general election as Clinton or Obama.

Hillary Clinton

Pro Battle-tested. The dirt on her is so old it won’t stick. Sensing history, women voters will come out in record numbers, including independents and Republicans who thought they never would. Steady debate skills would lessen Democrats’ jitters. Restorationist appeal: nostalgia for the 1990s, a third term for Bill.

Con The only candidate who can energize a dispirited GOP, which has been lying in wait for her. Surprise dirt will emerge, as it always does with the Clintons. Women would vote disproportionately Democratic anyway, offering little advantage. Depth of American misogyny unclear. Many Hillary-haters are the very independents she needs. Distaste for dynasties and a return of Clinton fatigue.

Bottom Line She can win, but she’ll need to run a near-flawless fall campaign.

Barack Obama

Pro Fresh, inspiring and embodies what most elections are about: the future. Heavy black vote could tip a couple of Red states into the Blue column, while those against him because of race wouldn’t be voting Democratic anyway. Teflon potential: Republicans would have to muzzle attack dogs or risk seeming racist. Strong with independents and college-educated men who have recently tilted to GOP.

Con Untested against Republicans, who would leap to define him before he could define himself. Name, background and lack of experience may represent too much change. Depth of American racism unclear. While polling shows liberal-bashing has lost its resonance, GOP would try it anyway.

Bottom Line A roll of the dice, but the only one with a decent chance for a landslide.