From what I've read, Soviet aviators liked the P-39 and P-63 fighters because of its 37mm cannon, good for taking out tanks. Americans didn't favor the planes so much because they had poor performance at higher altitudes, but was a moot point in ground attack. The Soviets didn't like the Allied tanks supplied to them as much as their own T-34 and KV-1 tanks (The Germans even copied the T-34 design in their own Panther tank). But yes, the most useful vehicles they received were trucks and locomotives. They got millions of cans of Spam, too.