Hello!
I've been using Systemcheats on and off for a while for both MW and MW2, and I've already written a short and sweet review for MW, so I thought I would make one for MW2;
Straight to the point: Systemcheats is definitely the best you can use, bar none. I haven't had any issues with the loader, the ingame menu, absolutely flawless from start to finish. Its fully customizable and configurable for Warzone, DMZ, and Multiplayer, and I have nothing to really suggest to make it any better, as Todd Howard would say; "It just works.".
If you want preem features for tons of games for a really good price, and don't want to try doing research for sketchy resellers or shops that charge super high prices for mediocre, featureless, potentially detected or even ripped off code? Systemcheats is definitely what I would recommend.