So far I found that the gear heads are the most difficult to play against. They have some you have ot snipe , some who stay mid range and work there way toward you, ones who run at you, and then The armored ones that take a minute to beat. I'm only about 3/4 of the way throught the game but I am impressed with the variety of the gear heads.

get ready for jackals..they arent too hard but the variety of them is crazy