1. One that fits... half the battle
2. Does the jobs you want and where it is compromised, that compromise is liveable
3. Power source and shot count
4. Single shot or mag system and how good is the mag system. Are additional mags an arm and a leg and easy to maintain.
5. Budget does it include scope, rings, bipod, dive cylinder etc.
6. Understand the common issues that a specific malke/model and Mk have.
7. Will it be a keeper and worth investing in a tune in the future like a Ratworks.
8. Will all your shooting peers point and laugh at the truly horrendous decision you make........