Activision is the publisher that owns the CoD series, IF and Treyarch are the 2 main development companies who've been doing CoD for years.
Treyarch's typically suck. The IF games do great and are very well received, then Activision gets greedy and goes with Treyarch as a cheap developer and their games don't do anywhere near as well and people don't like them as much.
CoD - IF
CoD2 - IF
CoD3 - Treyarch
CoD4 - IF
CoD: WaW - Treyarch
CoD: MW2 - IF
CoD: Blackops - Treyarch
CoD: MW3 - IF (on hold due to the current lawsuits between AV and IF)
Look up the reviews and sales figures for each of the games and the IF games have consistently sold and reviewed much, much better than the Treyarch games have.