Tyroc's red costume was my favorite. The white one he started with, with the color, bare legs and pixie shoes, yikes. That would indeed qualify as my least favorite Legion costume! (Although there was an era when everyone seemed to wear tights and giant boxy-shouldered crap-brown 1950's-style leather bomber jackets, in which case, pretty much *everyone* was wearing my 'least favorite outfit' during that, thankfully, brief, time period.)
I thought Cos' bustier was funny, if only because he was hanging around with other super-peeps wearing swimwear (Saturn Girl and Dream Girl, for two examples), so it just seemed like sauce for the gander. But yeah, all superheroes in swimwear, who aren't at least bulletproof, need to smarten up... Shadow Lass looks sexy as hell in a full bodysuit, so there's no need for her to be wearing a bikini into combat. Her skin is blue, not blade-and-blaster-proof! She'd be a mass of scars!
Others come and go. Element Lad's green and blue costume with the phallic arrow pointing up and the metal pyramidal spikes on the arms was hilarious. Cham has never had a costume worth a damn (although Durlans apparently have the same color palettes of orange and purple as Carggites...). Mon-El's reversal of Superboy's classic colors is great, and never needs to be updated, IMO. Saturn Girl looks appropriately 'iron-butt' in her vaguely fascist 'thought police' uniform, more so when it's red and white than pink and white. Dawnstar can't win. She finally gets some coverage on her legs, and now her boobs are hanging out. Do you know what happens to a shirt with a boob window when you are flying at Mach 7 in atmosphere?
"What's that scrap of cloth?"
"Dawnstar's shirt ripped clean off her body."
"Again? I've got a spare in one of these pouches, I'm sure..."
"Here Dawny, it's a T-shirt that reads, 'I hit Mach 7, and all I got was (friction burns on my cleavage and) this stupid t-shirt.'"