I'd probably say Bard is overall the best utility caster besides Wizard, as the Bard's Arcane Secrets gives you a limited spell selection from any class, starting at 10th level. A little late, but getting ANY 2 spells you want is pretty nice.
A pact of the tome genie warlock might be worth looking into. You get 3 cantrips more than normal, from any spell list you want. The Marid subtype gets lots of control spells added to their spell list, you get ritual casting, the Genie vessel can be a handy base or safe space for the party, and at higher levels you get limited wish and wish.