I don't understand why anybody would want someone else to get an achievment/trophy for them. It's like fucking a cantaloupe and telling people you got laid last night. Anyways, MW2 was the last COD I played, and I have all the Vet modes completed from 2 through to that game. MW2 was tough for sure, but I think World at War was tougher. The toughest "fair" vet mode among those I played. Even worse was COD 3, because it was SO buggy. MW2 is a nice one to hang you hat on for sure. Not trying to start a pissing contest, just my opinion. For old school, Metroid and Mega Man come to mind. Demon's Souls plat. I bailed on CastleVania at the Grim Reaper. Such a frustrating game. This is one of the benefits of the achievments/trophies. It's so nice to have a record of this stuff. Dead Nation plat on PS3 and Vita is another one I'm proud to have done. There's more for sure, but that's few.
World at War was the toughest of them all, primarily because for some strange reason they coded the enemies to spam grenades.
While in the games before World at War you could cheese the majority of levels by sitting back and picking them off one by one, this one was totally different and had you running for different covers after every kill.
Fun, but irritating. Just checked back and I got the Veteran achievement for each Call of Duty game up to Black Ops 2.
Halo 4 Solo Legendary was a lot tougher than the Call of Duty games IMO.