If you count MegaMek, there isn't a whole lot that I've avoided. I'll try darn near anything against the bot to pass the time. When it comes to table-top though, I don't think I've ever actually put a Stinger or a Wasp on the table. I own at least one of each, but I've never played with them. Since I don't get to play TT all that much, when I do, I don't like taking situational or easily vaporized mechs, and the 6/9/6 bug mechs always just feel like a wasted slot to me. On the other end of things, I don't think I've every intentionally brought a 2/3 mech to a TT game. I've played them electronically, but I don't think I've ever put something like an Urbanmech down on a real table. I find them too annoyingly immobile, and leave them in the box.
Technically, I have plenty of minis that have never seen the table, but mostly because I ramped up on collecting them in the past couple years, but don't have time to get them into physical games. But that isn't really in the spirit of what the OP was asking.