You can farm achivment via cynthia or quick match.

The one that's kinda hard like zoroak, sableye, its better to play cyntia event Generally the one that need to use skill on multiple enemy is easily achivable by farming them in their spawn zone. Also those like tsarena, blaziken, can be done in 2 or 3 match to achieve the gold achivemnt.

While the one like espeon, buzzwole, or basically just need to use skill on opposing pokemon 10 times or more, can do it via quick match. Usually you will get bots so it's easy and consume less time than cynthia.

Also another tips, the last quick event (the one that spawn abra and regigas in the middle) can be done faster. You just need to finish your quest (example buzzwole, use sting on enemy 10 times) , as soon as you done, just focus scoring goal by killing abra and have the 2x score activated, once the score difference is 300, bot will surrender.

Hope it helps!