I think my favorite is the Muse's Robe, but I also like the Evening Gown, Golden Empress, Toolbelt, Fleet Uniform, and the Body Control outfit whose name I have forgotten. Not as fond of the Data Visor or the Holster Shorts, or the default. Haven't yet unlocked the outfits for Combat, Condition, Domination, Stealth, or Environment.
Only got the Data Visor once (and I was specifically studying to unlock it, wouldn't have trained that combination of skills otherwise). It was kind of a pain to unlock—I think I wound up spending 12 to 15 turns on getting it, as opposed to the six to nine for another outfit. Part of that was that I didn't think to wait until I had advisors for everything.
I found myself wishing the bonus was bigger for that one outfit, or that it unlocked at 10 rather than 15 of every knowledge stat, even though it's already significantly lower than the 25 threshold for the other skills.