Quality brand name cells will tend to be very consistent and work well together in a pack, while lesser cells can vary quite a bit and it's hit and miss ( they work fine individually, like in flashlights and the like... but grouped in a pack is a whole other game )

You need to size the pack to your application, if you have a bike that requires a 20 amp capable pack, you should have a pack that can supply that much without killing itself.

What motor/controller are you using ? and exactly what pack are you considering ?