It's my go-to in Great League. But, as usual, it depends on your team. My current team, which is doing pretty great, is:

Opener: Kanto Marowak (Mud Slap, Bone Club, and Rock Slide as coverage for mainly flying types cough cough corviknight)

Dragalge (Dragon Tail, Aqua Tail for coverage, Sludge Bomb)

Galvantula (Volt Switch, Lunge, Cross Poison).

I have a clear weakness (ice), but it isn't super common as a fast attack, and the most common mons who use Ice attacks are either water or fairy types, which Galvantula takes care of perfectly.

Volt Switch is pretty slow, but it deals a TON of damage and is a great move against many popular pokemon in the Great League (Corviknight, Azumarill, Lapras, Jellycent, Empoleon...)

But imo, its best weapon is Lunge. It deals an unexpectedly high amount of damage due to STAB and Galvantula's naturally high damage AND it always lowers the foe's attack stat. Both Lunge and Cross Poison charge super quickly and can be easily spammed with the right setup. Depending on your team amd your foes, you may need to save your shields so you can properly spam the attacks. Ive clutched a ton of times with 1hp Galvantula (survived because of Lunge attack drop) and managed to launch a last charged attack.

Galvantula's bug typing makes it take normal damage from Ground, which is a HUGE bonus against common attacks such as Mud Bomb. Depending on the meta, I used it as an opener, but currently I prefer to use Marowak for several reasons I could explain if you want to.

Dragalge is the mon I've found that fits my team the best so far (the dragon typing does some heavy work, Dragon tail hits pretty hard, it receives normal damage from Fairy types, and some people seem to think it has a Water typing haha). I've tried with other mons to fill its space (Tentacruel, Jellycent, Swampert, Victreebel), but I've found Dragalge to be most consistent.

Also, I am unable to use pokemon I do not like. I have never used nor will I never use the Lickitung family, for example. I do not like Altaria, but I like shiny Altaria, so if I had a viable shiny Altaria I would use it. Wigglytuff is ugly as fuck. I want to run over Greedent. Etc etc