I really like Banshee, but I was shocked to learn she was at a mere 0.53% usage on last year's published stats. I'm also really fond of Yareli and Gyre.
Frost is a highly under-rated frame. I don't understand why he's disliked so much. His 4 will do full armor-strip and is a great CC for headshot kills. Someone conscious about where they're putting bubbles doesn't get in the way, except for people who think they need to be the one to shoot everything on the map, even if there are teammates on the other side of the defense point who can do that.
My only complaint is that his 1 or 2 are somewhat redundant with the 4 when you have a lot of energy, but Helminth can take care of that. I like his 1 for immobilizing high-damage targets, though it became less useful with the Eximus rework.
Steel Path mobile defense, or excavation, Frost is my guy. If only I could freeze the defense target guy and make him quit wandering around. I still often take Frost for defense and just keep moving my bubble.