The best way to choose fresh beans is at a market that sells them loose so you can pick out pods of equal size (for uniform cooking).
Snap beans, when broken, should snap crisply (although the very thin haricots verts are not as crisp). If edible-pod beans are very stiff, or the seeds are visible through the pod, the beans are overly mature and will be tough and leathery.
Shell beans should bulge through a tightly close pod. If they’re sold shelled, the beans should be plump and tight-skinned. Shelled limas should be grass-green (chalky-white limas will be starchy). Favas should be a light gray-green.
See also our recipe for: Green Beans with Fresh Tomato and Basil.