I don't think I have a particular preference for type or material I just want to see it be designed well. I don't like over-gimmicked designs or really choppy and blocky looks with color use that feels random. So often people forget that less can be so much more.
Kuuga, Nexus, TimeRanger, Tiga, Maskman, DaiRanger are pretty good examples of the kind of designs for herosuits I do like. Den-O and Kiva's various forms, GaoRanger, Ryukendo are all prime examples of what I don't like.