My favorite uniform of all Trek
is Captain Kirk's wraparound from the first season, as seen in "The Enemy Within," "Charlie X," and "Court Martial." I even own a damn near close replica of it. Gotta change the braid to something a bit more accurate. Oh, and the ship's patch also needs to be changed out. Right now, it's the third-season more pointy emblem, not the rounded tip of the earlier seasons.
Okay, I'm a Trek uniform geek. There I admit it.
Then it's TOS in general.
Second, the TMP uniforms because of the variety they had.
Third, the first and second season TNG uniforms. I like the clean lines of Thesis design, although I would've gone with a more forgiving fabric. You have to be really fit to wear one of those puppies.
Finally, the utilitarian look of ENT. In fact, I loved the entire look of that series overall. The uniforms, the NX-01, and the sets.
But I gotta say, I'm loving the nuTrek uniforms.