MY favorite race has to be the Nords, since the game's location is their homeland and I just appreciate the Nords sense of honor and pride more so than any of the other races. My least favorite...well any of the elven races are my least favorite, except the Orcs who I don't in my mind classify as "elven".
From my favorite to least favorite:
1: Dunmer, Altmer, Redguard, Khajiit, Nord, Orsimer, Argonian, Breton, Bosmer, "Imperial".
2: Dunmer, Falmer, Dwemer, Altmer, Redguard, Ayleids, Khajiit, Nord, Orsimer, Argonian, Breton, Bosmer, Maormer, Sload, Imperial.
Should I include the Dremora? I heard they actually have some kind of a society. Anyway.
There are races that I didn't include.