Well, I means which X-man's costume and casual clothes always follow the trend of fashion. Probably we should put aside those "newly born"  ones.

Jubilee. That yellow raincoat is the height of fashion. 8 )

wolverine

Emma, Pixie, Storm, Nightcrawler, X-23, Beast, Gambit, Xavier, and Northstar and Anole obv.

Monet, Domino and Strong Guy dresses well for his build. Must be hell trying to find clothes! 

Way out of left field, and I'm counting him because of a loose affiliation with X-Force - Pete Wisdom. 

Dazzler!! Duhh!!

emma frost, dazzler, cant really think of a guy.

I so would have agreed with Dazzler if she were still at the peak of her singing career or Monet if she had less faux pas. , but now, I must go with my lady, Boom Boom.

X-23.

The ONLY heroes shown in any kind of fashion have been the members of X-Factor & X-23.  All the regular X-Men spend all their time strutting in their heroing outfits.  That isn't fashion; it's unimaginative & smelly!

Considering Psylocke used to be a fashion model, even heavily pregnant Wolfsbane shows more fashion initiative than the ninja swimsuit.

Gallery

Rogue is best when it comes to cowboy boots

Emma

Then most fashionable X-MEN are Wolverine and Rogue, she always had cool costumes and where she not costume, she look good too

Storm, Monet, Emma

Psylocke, Dazzler & Northstar

Gallery

Emma Frost, Storm and some of the members of X-Factor

I like the costume galleries of  Emma, X-Man, Dazzler, Jubilee, Polaris, Tabitha Smith, Amanda Sefton and Aurora respectively.

Emma. Less is more. xP

I'd have to say M or Storm

Clearly Monet.

Wolverine and Rogue are such a massive "NO". It's ridiculous

Dazzler. That was easy! Monet comes in a close second - she's really made an impression on me since the Generation X days and she keeps getting better.

I've never really found most of the X-Women that fashionable. Ironically enough, artists tend to try and make some of the more popular ladies look like models, but without fashion training, some of their 'looks' end up looking like majorly poor taste with questionable cuts, color schemes, bad hair length and etc making them look like bimbos.

Did someone really say Gambit? I'm losing my faith in humanity...

Dat Psylocke.
BB

Ororo Munroe aka Storm

Shocker

It's clearly Ultimate Dazzler.