Absolute favorite so far? Duplicato! Having a clone around to tidy up your house, do your laundry & clean the toilet really frees up family time lol.
https://i.imgur.com/0Oj2MxD.png
But I also love Repairio, Delicioso & Scruberoo (if only cause saying Scruberoo is great, but also because sims can clean themselves :D). Mischief spells are also great to cause mayhem in the neighborhood. But still, so far, Duplicato is the best. Haven't tried all of them yet though.
Favorite potion? I really like Nimble Mind, Forced Friendship & Transcendent Charmer, but as a person who uses "fill needs - entire household" cheat a lot, I REALLY appreciate the Plentiful Needs one the most, as a slightly less cheaty way to do the same thing ^^