COD 2 for mod matches and sniping matches since the scenery wasn't see through.
CODMW for 1v1 cage matches and sniping as well. Gaming with friends is a lot of fun. Actually took skill unlike the other newer ones.
CODMW2 was pretty good for the TEDDY BEAR hide outs. (a lot of people didn't realize or know the teddy bears were added in because one of the developers daughters died from cancer while they were making the game. she died with a teddy bear in her arms. The ones in the games are a tribute to her.)
and last but not least, CODMW3 was great, but still has some flaws, not enough maps with foliage or anything, it's all just urban warfare maps.
Black ops was one of the better ones i guess because the bot matches could go on forever, but they didn't make it very fair, it's like theyre using every mod in the book on veteran lol