Get one with a thick mesh rubber netting. It is faster to get the hook free. Get the largest net that will easily stow in your boat. Make sure the length is long enough to dip in the water without leaning too far. Extendable handles are nice...
Frabill is a good brand (if not a bit expensive).
There are knock-offs that work pretty good...
EDIT:
This is the economy model I use, and I can vouch that it will float for a short time, but long enough to recover if you are quick!
http://www.basspro.com/Bass-Pro-Shops-Go...OSSSELL_PRODUCTI like a deeper squared bottom (Conservation Series).