Something small, the smaller it is the easier it is to flip etc as there's far less moment of inertia.
A lot people build their own acro frames as you'll crash far more often being able to make a new arm out of a bit of 10x10mm wood is far cheaper. On the other hand you can get a Teslaquad from a guy called teslahead on www.multi-rotor.co.uk he even has a list of recommended components too.
Thanks very much, I'll take a look!