Never tried out a Gameshark, though I used the Missingno. glitch to duplicate my Master Balls and catch all of the Pocket Monsters, but that was because - considering I've beaten the game in two complete gos before - I wasn't taking completing my Pokedex seriously and was doing it for fun. Of course, I also duplicated my Rare Candy so that doesn't make me much of a better player. Oh, and I caught Mew without using a Gameshark, so that's fun. (Fortunately, my Yellow version hasn't been affected by the Missingno. glitch so I still play that version every so often to suck out whatever fun is left in that cartridge, which is why the fact that my R/B version have been cheated in doesn't bother me).
Any version beyond R/B/Y doesn't really interest me. Catch 120 or so in my Yellow version was hard enough work for a lazy player like me and I don't think I have the energy or patience to catch all 351 or whatever the new number is. I figured that I spent half of my gaming life playing Pocket Monsters anyway.