YOU are number six.
*ahem*
No doubt opinion will differ, but I'd suggest Milotic. No major weaknesses (only vulnerable to Electric & Grass but a base 125 SD does a lot to stop that), great selection of moves and decent special attack value (no pure annoyer/tank this one by any means). It's even mid-range in speed (base 81) so if you want one that is speedy you can manage it (Max possible with +Speed personality at L100 would be 287).
My usual set is:
Ice Beam/Surf (depending on team needs. Surf is usually best)
Confuse Ray
Toxic
Recover
Bloody hard to take down without a OHKO.