Halo3 or Call of Duty, should I make the switch?

COD4 has a buttload of more features to the multiplayer, the ranking system is a grindish but its there so it's enjoyable and makes you want to keep playing and ranking up and getting better weapons/attachments/camos. Halo multiplayer is more or less the same thing every match. not much variety and I feel that the game pace is slower than that of COD4 imo. the last time I played halo online, the matches were kinda laggy and there were very few ppl playing, (that or the match making system just blows).