Suggestions...?

Onix

Toss a curve when the circle gets really small. If you don't know how to curve it's by putting a little spin on the ball so it goes off to one side and comes back to the center. There are YouTube videos on how to do it. Excellent throw is landing a center shot on the target center when it gets really small. Excellent curveball is doing both on the same shot. Good luck!

Wailmer and Slowpoke are some common favorites of mine if you live near a water biome

Another good target is loudred.

Zangoose and Torkoal are personal favourites of mine. And if you finish a Machamp raid... he's a prime candidate for farming excellents, especially with a nanab.

Spheal is another good target for potential excellent throws.

use the banana berries as it helps on the movant of the Pokémon.

by the time I did the quest I was able to plant two ex throw curve on the 50th Pikachu to get my mew.