In case you didn't read all the articles on the subjects, John Edwards and Rudy Giuliani are out of the presidential race. This effectively leaves two candidates for each party to choose among. I know technically Mike Huckabee, Ron Paul, and Paul Gravel are in the race still, but all three of them are thinking about something other than being president at this point. Huckabee wants to prove that John McCain needs him for VP. He would be great in a VP debate and a great surrogate, but same part of the GOP that hates John McCain on economic issues also hates Huckabee for the same reason.
Ron Paul might as well start saving up those millions to get on the ballot in November as Libertarian. Sen. Gravel should just take a bus home.
So who gains and who loses with the departures of the two serious contenders for the nomination? In the short term, Obama is hurt the most by Edwards' leaving. Ideally for Obama, Edwards would have hung around to attack HRC in debates while siphoning off white voters from HRC to ensure Obama wins states like Oklahoma on February 5th. As others have pointed out, he was probably the best debater out there of the three of them, or at the very least the second best. Now Obama needs to get better at debating in a hurry, because Hillary is looking forward to smacking him around on CNN. In the long term, perhaps Hillary loses the most. Perhaps that fabled ABH vote (anybody but Hillary) will coalelse behind Obama and he can get more states than he otherwise would have, especially if Edwards gives him his delegates, endorses and campaigns with him. Obama certainly wants his endorsement. He lept out of the gate with a fawning farewell statement. Ideologically, Edwards 2.0 is much more like Obama than HRC.
On the Republican side, Giuliani's departure certainly helps McCain the most. The two were both relatively moderate Republicans on just about everything except foreign policy, where both want to start a war with Iran and stay in Iraq indefinately. Rudy's endorsement should insure that NY, NJ, CT, etc. all go for McCain. Romney is in serious trouble because almost all of the Super Tuesday states are winner take all on the GOP side. Which means that, unlike Obama, he can't content himself with 45% of the vote in some state and draw about the same number of delegates (or if he targets optimally, get more than the popular vote winner). Romney has to win outright in pretty much any state besides CA to get those delegates. And even though he still does better among conservative Republicans than McCain, there is too much momentum and elected officials behind McCain for Romney to stop.
While Obama's path to the nomination is very difficult, it is still plausible, especially when you hear things like Connecticut being now effectively tied. By contrast, I just don't see how Romney gets back on top after narrowly losing Florida.
The question now becomes, who would each side match up best against, and who would be the best VPs for them. For Hillary, I think she is stuck with picking Barack if she gets the nod. No way any party head will let her pick a dud like Evan Bayh. On the other hand, Obama can't pick Hillary because it would undermine his message and overwhelm him. Does he pick Kansas Gov. Kathleen Sebelius, who endorsed him and reminds people that his mom's side of the family grew up in Kansas? After the bland SOTU response, I think she is done. Bill Richardson is similarly too gaffe prone. John Edwards doesn't want to be second banana again (but he would take AG I think). Barack needs someone with Washington street cred without undermining his change/unity message. NYC mayor Mike Bloomberg? Not unless the FEC says he can spend all of his money on the race. VA Sen. Jim Webb? Fits with the appeal to "Reagan Democrats" and change message (especially on Iraq). If he wants to get the mini-me, like Bill Clinton did in 1992 with Al Gore, I would say Newark mayor Corey Booker: a charismatic black mayor who whites like and is trying to make his notorious city better. This fits in with the stories of Obama working in the projects prior to law school, since Booker lives in one.
As for McCain, he has to pick a social and economic conservative, even though McCain is pretty solidly pro-life. I would say someone like Sen. Sam Brownback. But if the Democrats nominate Obama, McCain needs his ticket to get young fast, but not Dan Quale young....we are going to see a lot of basketball games if Obama wins the nomination. If McCain picks Sen. Lieberman or Sen. Graham, he is just asking for a whooping. Romney I think would pick Huckabee because of his appeal to evangelicals, whom Mitt needs to be back on his side for November.