Pistol with tons of bonus critical damage for Una, new version of TK's Wave from the first game for Hyperion. I always go with Una since I like the pistol better, and giving the plans to Hyperion is a jerk move.
They're both relatively unplayable and you'll likely already guns better than both.
Unless you use other means than farming to get your guns, the Hyperion pistol is actually great. It has +400% critical damage. It get's about 15 shots of great accuracy. I used this gun alone to farm Dukino's mom for a while. I killed her before she got in range to attack me. This was on playthrough one, so before bee shield and cc. So far it has been my favorite gun in the game.