I really like psi armor on 1-2 guys. My experience is that psionics are not common enough that you can have 4-6 colonels with 100+ base willpower. I usually have 1-2 guys in psi armor near the end since that gives 100% mind control on muton elites and heavy floaters.
I've also take to using flight armor for my snipers, since I prefer the height advantage to the guaranteed crits from ghost.