I personally always get a Starly because Staraptor is great! But Crobat is also easy to get and can be helpful and Altaria is a great ingame wall.
Staraptor- High Atk/ Speed but limited movepool. Good for spamming Close Combat and Brave Bird with Quick Attack as a revenge move.
Crobat-rounded stats High Speed. Decent movepool and good for status (confuse Ray/ Toxic/ Hypnosis[if you breed]) but weak STAB and coverage moves.
Altaria- Good Def/SpD stats. A rounded movepoo with good defensive moves and his only real flaw is his lack of attacking power.
I ahve usedall of them and they all work fine, so the choice really is yours and how much time you are going to put into leveling them up.