What will be the closest state

[pbrower2a]

Closest to the national average -- Ohio or Colorado. Such will hold for a bare Obama win or loss in the Electoral College.

220 EV for Obama -- Michigan or Pennsylvania.

250 EV for Obama -- Iowa or Wisconsin (shades of 2004)!

310 EV for Obama -- Florida.

370 EV for Obama -- Indiana or Missouri... maybe Arizona.

(Nobody has won between 57.1% (Truman 1948) and 65.3% (McKinley 1900) of the electoral vote since 1880, so if Mitt Romney sees himself losing  323-215 he is going to do some gambles and risk losing big or getting much closer. That is how John McCain acted in 2008, and he ended up losing badly by betting everything on Pennsylvania and losing a raft of states in the process.

400 for Obama -- Georgia or South Carolina.

410 to 450 EV for Obama -- Texas. 38 electoral votes in that state alone, a giant state with no good analogue.

Beyond that I can't make too many distinctions between the states.