From the NBC blog "First Thoughts":
Obama vs. McCain
Base Obama: CA, CT, DE, DC, HI, IL, ME, MD, MA, NY, RI, VT, WA (168 electoral votes)
Lean Obama: NJ, MN, OR, WI (42)
Toss-up: CO, IA, MI, MO, NV, NM, NH, OH, PA, VA (112)
Lean McCain: AR, FL, GA, LA, MS, MT, NC (81)
Base McCain: AL, AK, AZ, ID, IN, KS, KY, NE, ND, OK, SC, SD, TN, TX, UT, WV, WY (135)Clinton vs. McCain
Base Clinton: CA, CT, DE, DC, HI, IL, ME, MD, MA, NJ, NY, RI, VT (172)
Lean Clinton: AR, MN, OR, WA, WI (44)
Toss-up: FL, IA, MI, NM, NH, OH, PA (101)
Lean McCain: CO, LA, MO, NV, VA (47)
Base McCain: AL, AK, AZ, GA, ID, IN, KS, KY, MS, MT, NE, NC, ND, OK, SC, SD, TN, TX, UT, WV, WY (174)
This is all very preliminary with a lot of unexamined assumptions, but it provides a place to start, and it identifies where the battle ground states are likely to be.
(One of the assumption is that the math is correct. When I add up the electoral votes for the base Obama states I get 181 rather than NBC's 168 -- and Clinton should get 187. Not sure where the discrepancy lies since NBC doesn't identify the electoral value of each state. I'll assume for now that NBC is better at math than I am, but if someone wants to take the time to check the numbers, I'd appreciate it.)
I'm sure this map will look very different once the campaign starts, and I would not be surprised if many of the tossup states in this configuration start leaning blue. I just think that general disgust with Republicans is a factor that is not reflected in this breakdown.
But assuming NBC is more or less correct, against Obama McCain gets 216 red and red-leaning electoral votes to Obama's 210. Against Clinton McCain gets 221 to Clinton's 216. So he has a slightly better red or red-leaning base than either candidate. Arkansas's 6 votes make the difference between Obama and Clinton in terms of likely blue voting states. It is likely to go to McCain if Clinton is not the candidate.
According to this analysis, Obama is stronger than Clinton only in WA-11 while Clinton would be stronger in NJ-15 and AR-6. But both WA and NJ will likely go blue no matter the candidate. As mentioned already, Arkansas is the one state that would probably go to McCain if Obama is the candidate. GA, MS, NC, and MT are more competitive for Obama than for Clinton, but lean red. Clinton will be more competitive in FL, which is a tossup for her leaning red for Obama.
Obama has a better chance in CO-9, MO-11, NV-5, and VA-13 (total 38) if he is the candidate, because these states, according to NBC, all lean toward McCain if Hillary is the candidate. And Hillary has only the advantage of AR-6.
So the question becomes: who will do better in the other tossup purple states: IA-7, MI-17, NV-5, NM-5, NH4, OH-20, PA-21? Assuming Obama takes CO, MO, NV, and VA, he will need 22 more electoral votes to get to 270; Clinton, assuming she takes FL-27, will need 27 to get to 270. That means that both Clinton and Obama would need only one of the big purples--OH, MI, or PA and Obama and one of the smaller states.
What's the bottom line? It would seem that the critical battle ground states will be OH, MI, or PA. That would make the PA race a little more interesting this month, and it also raises questions about whether MI will support Obama. But bottom line is that I think either Dem candidate would win. It's just a question of who would be the better president, and I've been pretty clear about my preferences in the matter.
P.S. Here's another site that might be a useful resource in tracking electoral trends. It assumes that Obama has won the nomination and has him starting with 174 base votes to McCain's 149 with 215 undecided.