For me I'm going back and forth with Ash and Loki.
I'm trying to build up a stealth character. Both of them has their ups and downs. At the moment I'm trying to build them up to see who will be the better stealth Warframe for me, and after that I'm going to get a engineer Warframe called Vauban... I like to call him the Isaac Clark Warframe
He looks perfect for defense missions.