I was kind of let down with the 343i customization tweaks. I really enjoyed the Reach and I guess I got spoiled with it. So, I'm pulling from CE to Reach.
(Originality-wise) However, ODST is really iconic. Shows up in most of the games and had a mythic aspect that feels great. The face of the venerable shock troopers is definitely cool.
(Myth-wise) Recon is another great one. Starting its life as a Bungie exclusive and becoming available to the public. The style is sleek, lean and cool. Definitely a good one.
(Style-wise) Personally, I rock the Air Assault variants. The helmet generally fits my style choices and never obscures the overall look of a character. Originally designed to be a replacement for the ODST, I like to think a Spartan may utilize this as a field upgrade to the ODST hardware.