Gotta be BF3. BF2142 was my first shooter, and it is what got me lovin the genre.
Call of Duty 4 and WaW were good, but the last two have been suckfests. After MW2 I gave BO a chance since it was treyarch, but they've proven that all they do is copy the garbage infinity ward cranks out.
I did like cod4 and WaW better than BC2 though.
For me 2142>WaW>Cod4>BC2>BO>MW2.
To be fair, WaW and Cod4 are pretty much equal since WaW is just a WWII skin of Cod4, but I am the jesus at WaW, so that is why I rank it higher. I didn't put BF2 in there since I only played like 10 hours of it. I got it for free from my friend, and I was already into 2142 at this time.