To be perfectly honest, still the best helmets have to be the Mark V and VI. They are the real helmets. The other helmets are Bungie's modeling guys having fun in Milkshape and 3ds Max.
My favorite armor (and the one I'm striving to get)? Mark V helmet (don't have), CQB left shoulder (have), Mark VI right shoulder (have), CQB chest armor (have). Or alternatively, ODST Helmet (don't have), CQB left shoulder (have), Mark VI right shoulder (have), Mark VI (or CQB) chest armor (have).
And go either red, white, and blue, or orange and gray as the color scheme!