Duskblade for at least 3, for the Arcane Channeling. If you are going to gish and have higher level spells than a Duskblade normally gets, you can fling those spells with your sword.

Question is...why are you losing 4 caster levels? Your aim should be to take the bare minimum in order to get into a Gishy PrC like Abjurant Champion or Spellsword or even Eldritch Knight or Knight Phantom.