Hi mate 250 mm is a mini quad fun to race fast , 330/450 is a normal size quad( starter size ) ie DJI Phantom flame wheel etc , 550 upward are large quads most are camera platforms as they are stable can fly very slow , there are micro quads like the hubsan x4 nano qx etc good for indoor flying
the one in my pic is a talon v2 but is 700mm not the standard 550mm , i put my wrist watch in the pic so gives an idea of size ( its big)