For each Republican candidate, I rank the Democrats by their margin of victory in the last Rasmussen poll. Edwards is the strongest, followed by Obama, and then Clinton.
Rassmussen national general election matchups
Edwards also tends to be the strongest candidate in the SUSA state matchups.
Brownback
Obama +15
Clinton +8
Giuliani
Edwards +8
Obama +5
Clinton +1
Richardson -3
Dodd -5
Kucinch -12
Biden -16
Huckabee
Edwards +17
Obama +9
Clinton +8
McCain
Obama +5
Edwards +4
Clinton +1
Richardson -5
Biden -13
Clark -18
Dodd -19
Paul
Obama +20
Clinton +15
Romney
Edwards +11
Clinton +9
Richardson +8
Obama +3
Tancredo
Obama +17
Clinton +13
Thompson
Edwards +14
Obama +6
Clinton +5
Biden 0
Richardson -1
Kucinch -6