Just taken a more detailed look at those poll figures 
Some of the discrepancies are truly alarming. I didn't spot the slant at Romney first time either. I take it Trackside isn't based in Salt Lake City.
My best guess is that Republicans would least like to face Edwards, and most like to face Obama. In Giuliani they have a candidate who I think could beat Clinton, especially in set pieces (although these are usually so choreographed and scripted its difficult to establish an advantage in them). My spies tell me that she's not coming across as quite so frosty as she has done in the past, and isn't getting tripped up on some of the more complex issues either. I really can't see any of the Rep candidates beating Edwards though (all things being equal - which of course they never are). My best guess, is that in a long haul, Rudy would beat Hillary, or is the only candidate capable of doing so, but guess is all it could be this far out.
I'd expect Obama to be the first 'big hitter' to drop out of the Dem race, and when this happens in the campaign will be crucial. If Hillary's been able to build up momentum by then, then it might be too late, but quite where his support will go would be critical. Most people hold an opinion on Hillary, and they tend to be polarised between top gear and reverse. Despite the fact that his voters would seemingly have more in common with her, my instinct is that they're disproportionately likely to shift to another candidate. Afterall, if they aren't already voting for her, there's a better chance than there is with most candidates, that the reaosn is because they don't like her. I'm not sure she's the sort of person whose going to pick up second preference votes in bucket loads, and a compromise candidate would stand to be the beneficary, which as I said, could generate momentum at a crucial time, depending on when Barrack calls it a day, and whether he endorses anyone in doing so.
I seem to think Edwards tried this Washington card on John Kerry late in the day in 2004 too, but then Bush played it very successfully in 2000, so it obviously can strike a chord somewhere.
To be honest Obama and Edwards are the wrong way round at the prices, but it's starting look like Giuliani's going to be lining up in the red corner, with Romney as the biggest threat. I've always had the impression that Rudy's a bit accident prone though, but I'd never under estimate what he's capable of
