What is your least favorite aspiration?

Public Enemy because I don't like the idea of someone aspiring to be a criminal.

Hard to say, I've enjoyed the ones I've played around with, and the others, I haven't played with enough to have a solid opinion on them, but I agree that Mansion Baron can be annoying.

Friend of the Animals. It's difficult in a way that isn't enjoyable at all

Painter aspiration because it's easy. Public Enemy is one of the best for me. :D

I haven't played them all so I can't really provide an informed answer. I haven't disliked any of the aspirations I have chosen to play to completion, but then I have chosen them because they appealed to me and suited the story and character of the chosen sim. That includes the Public Enemy aspiration. >:) I have less interest in the Fortune aspirations though and I'm not sure I wouldn't find them slightly boring. I haven't completed Serial Romantic either because it just doesn't appeal to me or suit any of my main sims (I'm a hopeless romantic and prefer playing Soulmates), although I have chosen it for others. I'm going to tackle the Outdoor Enthusiast one soon, but I hope it won't get too frustrating hunting for all those plants! I really like the Family aspirations, but because you have to have at least 3 children and/or adult children for them I haven't been able to complete them, as often I don't want more than 2 children or to even age them past the child stage if they're a vampire or ghost. For that reason I've sometimes chosen one in CAS to suit the Domestic sim, but then changed to something else as the goals just don't fit in with my plans.

Both Love aspirations. Soulmate is all about dates, dates, dates, and more dates - incredibly unimaginative, repetitive, and boring, and all you get for it is a trait that makes dealing with conflicts easier, as if conflict was ever a thing in TS4. Serial Romantic is a relationship grind fest even worse than Friend of the World (although I don't enjoy that aspiration either) because the romance bar is harder to fill up than the friendship one.

@annaliese39 never tried the outdoor enthusiast. I also imagine it might get boring with all the collecting.
@GrumpyGlowfish that is a really insightful question, why having a reward to help on something that is definitely not a problem in Sims 4. Actually it's a problem that it isn't a problem.

Public enemy is my least used but I did do it once for not so berry, it was fun but I don't like playing evil sims mainly so it's rarely used.

Party animal is one I find annoying cause if I don't already have boosted parties I usually run out of time for the gold medal

I've never completed a single one! I don't tend to take much notice of them.

Other than the aspirations I will never try because they don't suit my game play (like criminal or love), I dislike the parenting aspirations most. I'll use them when there are young children in the house, but they literally take a lifetime to complete.