Didn't say my favorite. Obviously Highrise, which seems kinda similar to one of my favorite CoD4 maps: Pipeline (because of the tunnels) but then again I liked almost all of the CoD4 maps. Anyway, I like Favela because it's pretty balanced and easy to hunt down boosters. I like Skidrow because it is also balanced.
My favorites are Skidrow, Salvage, and probably Rundown. All because they are decent sized maps, where you can run and gun, snipe, or use an assault rifle.