The first criteria should be suitability of the craft's design for the purpose you intend for it:
- do you want to fish from it or use it as transport in rivers?
- what class rapids can you expect (worst case)?
- will you carry stuff along?
- how will you get back to the car?
- puncture resistance needed for conditions (rocky bottoms, debris, etc?
Then portability and inflation ease:
- how much does it weigh?
- how compact does it pack?
- can you inflate it first at a gas station and bring it to the water?
- does it have fast-deflating boston valves?