The V4-6 were the best. High quality lasers and no double check protection. They also can use the old gameshark disks too. If your going with a no-solder mod or a flip-top and swap magic disks, those are the best. They are increasingly rare though. With a real mod chip, I don't think there is any difference between V4-9.
The laser burnout issue is with the slimline PStwo, all other versions should be fine.