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.
I play a lot of Equinox and Octavia, but I very rarely see anyone else bringing them into missions.
I don't think people want to farm Equinox, and don't know how busted her day mode 4 is.
I have been playing less Octavia lately even though she's still a favorite, because she's so powerful that it makes things boring. I just sit there twerking to maintain invisibility and refresh skills once a minute or so.