I'd go with Jynx personally. Between Xatu and Jynx, the latter cleans up. It has STAB on both Ice Beam and Psychic as well as Lovely Kiss which is 75% to put your opponent to Sleep. Her Special Attack is very strong and she has good speed so there isn't really much to complain about.... except for her defense. However Jynx outspeeds most things which therefore means she can usually put things to sleep before she gets hit.
As for a moveset, I'd go with this:
First three are really your bread and butter. There are a few options for the last move though I would go with Attract; use it after you put an enemy to Sleep and it will offer you a good chance to avoid an attack when it wakes up which will allow you to reapply Sleep.... in my opinion pure evil
. Reflect is there to help out your defense... but Meganium could do it for Jynx. Mean Look will prevent switching and should only be used when you know you can outhit your opponent.