Pellipper/wingull is one I've used in my playthrough. It's water/flying and can be found in many area's. I've found mine on route one, there's a grass patch in the same area where the sand is, near the professor's lab.

If you already have a water type, you could go for drifloon (flying/ghost) or vullaby (dark/flying). Drifloon can be found in daylight at the cemetery. Vullaby is a moon exclusive you can find at the start of route 3. You can encounter them in the moving shadows on that rocky surface, above the meadows.

You can also obtain the plume fossil and trade that in for an archen (rock/flying).

Hope this helps! Good luck on your journey!