Go with Kyogre or Lugia. Both of them are beasts. A Water Spout form a Specs Kyogre can 2HKO Blissey.
I actually tried out Trachy's Tauros a couple weeks back on Shoddy, and it seriously messes up the tier. Nobody expects it, and it ruins everything in the tier. Screws over the dragons, it hits back the Dragon Trio pretty well, it messes up Deoxys-S, totally murders Ho-Oh, sweeps Latios, Wobbuffet, and Shedinja like nothing, as well as severely weaknening Darkrai, Deoxys-A, and even the odd Ubersect. It's seriously a beast.
If you want a really user-friendly, usually risk-free choice in Ubers, then pick Rayquaza or Palkia. Ray's really fast, has great sweeping potential, and gets the always-envied Extremespeed alongside STAB Outrage. It's a very potent threat. Palkia is basically the same except no x4 weakness.