Dynaman is my favorite Super Sentai hero costume.
I'm aware that this was originally going to be a baseball-themed series (Baseball Task Force V-Leaguer), but it just proves my theory: sports equipment looks better on superheroes! Even The Electric Company's Letterman! I can actually see a superheroic science team wearing something like this (the baseball helmets are like open-face motorcycle helmets or hardhats)!
I also love Goranger, which have the quirkiest designs ever. Unlike anything after JAKQ, they're made of either leather or vinyl, and have very wild designs. In a way, they also look sort of like the Mysterians!
Battle Fever J is great, too! Like no other team design before or since. (X-1 Mask from Maskman is an exception.) I especially love the robot-like faces with two eyes (making this, IIRC, the only Super Sentai team with two eyes on each mask, as opposed to visors)! This was the last in-house Toei design before Bandai completely took over (because Tooru Hirayama left Toei Superheroes after this series).
Among other favorites are, off the top of my head, Bioman, Changeman, Flashman, Maskman, Liveman, Fiveman, Jetman, Zyuranger, Dairanger, Kakuranger, Hurricanger, and Boukenger (which, in a way, recalls the Dynaman designs!).