Gotta be R2: he actually has not only space combat mechanic feats, but also actual ground combat feats that require ingenuity and make use of more advanced tech than C3PO or BB-8 (jet propulsion in Attack of the Clones to help rescue Padme and utilizing spilled fuel with jet propulsion to catch the battle droids on fire in Revenge of the Sith's opener).
F*ck that I want HK-47. We can kill some meatbags.
__________________ Chicken Boo, what's the matter with you? You don't act like the other chickens do. You wear a disguise to look like human guys, but you're not a man you're a Chicken Boo.