My favorite is easily the maroon TWOK-forward uniforms. They're the most reminiscent of an actual military uniform. As a result, my uniform (which I've tried to make reminiscent of Battlestar Galactica and several real-world Navies) is based on this uniform. I'll post pictures when I get home from work.
After that, my favorite are the TNG movie/Season 5+ DS9 uniforms with the gray ribbed shoulders. Less militaristic than TWOK, but a runner up in aesthetics for me.