My difficult child 2 has been taking Depakote ER for about a year now. I don't have anything esle to compare it to, though so I can't help much there. It has helped his mania symptoms pretty well so far. He recently added Seroquel XR and it is helping with his angry outbursts to a certain degree, as well as his attention, of all things. Although I don't think he's at a high enough level yet.
Like Smallworld said, you won't know if the new medication is better, worse or indifferent until you try it. That's the biggest problem we all face in trying to find the right treatment for our kids (or ourselves!)...
psychiatrists typically know their psychiatric medications really well, so hopefully the reasons yours has for switching your difficult child are on target.
Not knowing your insurance situation, have you shopped pharmacies in your area for pricing on the new medications? Some of the warehouse chain pharmacies are known for lower prices. There are also mail order pharmacies...