Sentinels, Scrappers, and Stalkers (basically anything other than Tanks, Brutes, or Kheldians) imho have a better chance of staying alive by playing a softcapped defense based build over a strictly resistance based secondary because those AT's have a lower resistance cap than the 3 AT's I excluded (note: Kheldians have an 85% resistance cap as opposed to Tanks/Brutes 90%).
That said, a set that layers your damage mitigation usually works extremely well also, such as Willpower or Bio Armor.
I personally have 2 lvl 50 fully IO'd Sentinels, one being a Rad/Rad/Elec (which is really strong and fun to play, rad armor is great), and an Elec/Fire/Psi (which I made on a whim to try out electric blast with Molten, it's also fun and decently survivable given the sapping nature of it's electric attacks).