Evolve Magikarp now or later?
Should I evolve this Magikarp now, or wait till Gen 3 when Gyarados possibly gets Waterfall?
Edit: These are my good CP/IV Gyaradoses that I already have:
1: CP 3008 IV96 L34.5 DT/O
2: CP 2776 IV91 L30 B/Cr
3: CP 2490 IV87 L27 B/HP
4: CP 2173 IV89 L23.5 DT/HP
5: CP 1907 IV93 L20.5 DT/O
I have only 300 Magikarp candies. But I can easily get the remaining 100 candies by grinding karps for a while tomorrow.

Answers
Agree, I evolved my shiny karp yesterday, got DT/HP (very happy). He still needs to power up, but that can wait. And if you get HP now, even if they keep it in the moveset, it's an easy QTM to get waterfall (or 2 if you're unlucky). If you don't get it, the CTMs are a crapshoot, before or after Gen3.
Personally, I don't have DT/O Gyarados, as I don't see the point - there are way better options to take out Dragons (like Ice, Fairies, even Rock is more effective.) But DT is a great general quick move. Hopefully Waterfall will be a better specialized move, making Gary relevant again (since the old days when high CP dominated the gym scene, even if he wasn't a great attacker or defender for his CP).