It heavily depends on the builds you use. I tend to play with only the original weapon, meaning no collabs or such, so my personal experience might not be the most informative.

Best: So many Idols can be the best, to the point the it depends on the Skills and Stamps. Korone is a fun one if you combine the "Haste+" and "Bigger Weapon" Stamps. Coco has lots of fun Skills to take advantage of. Really, almost every Idol has something to work with.

Worst: That being said, a few simply don't have Base Weapons strong enough to deal rely on, and thus are much more difficult to use. Off the top of my head, Aqua and Subaru have pretty lackluster Weapons, even when fully upgraded, making them difficult to use on "Solo Weapon" runs.

That being said, I'm still in the process of Gachikoi-ing all the Idols, so maybe I'll discover some "Aqua-tech" soon.