Advanced Wars! I played a mean Grit (didn't everyone?) but was pretty lousy at the strategy part. I loved that two allowed for custom maps; my favorite was 3 very-poorly-supplied teammates against one super-decked-out AI. You started with one mech and a lander with your HQ on a remote island and had to creep onto the mainland and start guerillaing bases and factories. Lots of trees and mountains to make Fog of War a big factor and man, so many afternoons trying to take down Super Kanbei on that map.
Advance Wars DS is still in my library for a reason.
Advance Wars DS is still in my library for a reason.