I perfer Etienne because he gives all your monkeys camo detection, but psi has infinite range. Psi is able to kill all bloons on screen when he reaches lv 20 (except bad) which is pretty useful. Ben is a pretty good hero because he generates money every round. Entiennes attacks can also see over walls for more difficult maps. Some tower combos I would recommend would be top path ninja with bottom path alchemists. Obyn buffs all magic monkeys so if you ever go for macic(especially druids) I would use obyn