Advice for multiclass - Rogue(Thief) 3/ Full Caster X

The new thief feature, being able to use a magic item with a bonus action, seems like a great feature to add to a full caster.

What I'm trying to figure is which full caster to go for. I'm trying to pick between Bard, Wizard and Sorcerer. I'm a leaning a bit more towards Wizard because we already have a Bard in our party and this way I can take care of Investigation and Int related checks. But Magical Secrets and the Valor Bard Extra Attack make Bard seem quite attractive (pun intended), and metamagic is pretty cool as well.

All of these seem like pretty good options to me. Having trouble deciding.

Waddaya think?

EDIT: To clarify, I'm going ONLY 3 LEVELS in Thief. The remaining levels will all be in the caster class. It should be Full Caster X/Thief 3. My bad.