Short answer: Neither
Long answer:
Flamigo has good-ish stats at 115 base Attack and 90 Speed (only average), but only has access to Close Combat and Brave Bird (the only two moves that actually allows you to sweep in this game) only late game (7th-8th Gym), and its Fighting/Flying type has 5 weaknesses, some of which (Flying and Electric) have Pokemon that can easily outspeed you.
Corviknight, on the other hand, is slightly better. It has 105 base Defense, but all else about Corviknight is not good. Due to it having only a base attack stat of 87, all it can do is to use Iron Defence+Body Press, which will not work against Ghost type Pokemon. On top of that, a speed stat of 67 makes it weak to any half decent sweeper.
All in all, both Pokemon are not really good if you are finding a bird for your team. If you need one, you can use Kilowattrel or Staraptor, both as easily gotten as the above two.
Hope I helped!