If you want hardy get captive bred/ aquacultured clownfish. I don't know how long they live though, but I bet captive bred/ aquacultured ones live longer than wild caught.
Like ViPeR said get Aquacultured. You just never know how old they are already if you get wild caught. I am not sure anyone knows exactly how long they'll live. Depends on your ammonia levels!
Most Clownfish species are very hardy once acclimated to a new environment. I really don't know what the toughest Clown would be.
Most Clownfish can live 20 - 25 years in a captive environment if they are well cared for.
