Clint Barton as Hawkeye is the guy who plays with the big boys. Obviously, he has elite training and can do very impressive work with a bow and arrow.
Drax doesn't come across as particularly intelligent because he always needs to say the exact truth and what's on his mind.
Groot, while he may have a short vocabulary, is an ultra-intelligent, tree-like creature from a species called Flora colossus.
Bucky Barnes is another hero who was created with Super Serum, making him the Winter Soldier.