The different companies use different materials and geometries for their frames.

So all make good bikes, but that depends on what "feels" right for you.

For me, i need a small frame but some companies make smallish frames but either the standover or the forward reach are still too long. So that usual limits me to only a few types of bikes.

The best thing to do is to test ride. Its very hard to decide on a bike if yo uhaven't even sat on one.