My favourite piece of uniform in any Star Trek is this snazzy T Shirt worn by Kirk.
Simple, elegant and it still looks fashionable today. But most importantly, it is a good fit for Shatner. In general, I think we are all accustomed to better fitting clothes nowadays, and so shows made in previous decades look a little outdated. Some styles worse than others, of course. Dare I say it, the outfits in the new movies have been great. I wouldn't change them at all. I like Starfleet having big bold and bright colours. Darker colours look more militaristic and less Star Treky. So I think I prefer the TNG uniforms to the later darker look. Though the darker uniforms fit the actors much better in my opinion.