I have two good Garys, a 96% that is my main at 3115 CP with DT / HP (13 / 15 / 15). Another more recent is a 98% with Bite / Crunch - this one is only at 1960 CP.
I also have a Magikarp that is only 88% but 15 attack, and I have the candies to evolve it.
The question: with Waterfall available, should I TM my main Gary's quick move? Or should I evolve a new one, costing me many candies and stardust to power up? Is having a DT Gary worth it to keep? I also have a 80% Gary with 15 attack that has Dragon Breath / HPump. What about my Bite / Crunch Gary - with there be more uses for it in the future?
As an aside, I have a shiny Magikarp (although only 58%) that I might like to evolve someday, and I wouldn't have the candies to do it once I evolved a new one. Magikarps don't really grow on trees around me.
You definitely want/need a WF/HP Gyarados, so yes, TM the main one. You will then have the premier water attacker in the game, and it will be useful in a lot of situations. It might take two TM's, but if you have them to spare, it's a no-brainer.
DB is rare on Gyarados, having been made legacy very early in the game, so I'd keep that one, and maybe TM it to try to get outrage. Then, you'll have a nice team of double-water, double-dragon, and double-dark Gyaradoses.
I would keep the DT one (it's legacy and is good for defending and fighting Dragon-types. Maybe even TM it to Outrage.
TM the 98% for sure. Bite/Crunch has Dark-type synergy, but both are pretty terrible moves. Crunch is especially a horrible move, especially since Gyarados has no STAB bonus from it.
