So I've been using Excalibur since that's what I picked to start. It's awesome and feels really strong.
I linked my twitch and got the frost frame. Umm... I don't get his power set. I only have the first power but it feels like it's a single target hitscan? I'm not sure yet on this frame but it doesn't feel as good.
Frost is a slower, tankier frame and among the most popular for defense missions because he pretty much trivializes them up until late game and is still powerful afterwards. His 1 is mostly used to destroy globes from his 3rd ability.