Both medications were originally used to control seizures. It's generally accepted that Depakote is more effective with bipolar.
I have taken lithium and depakot and now take tegratol. Tegratol has been a miracle drug for me. Depakot (2000mg) only made me fat and eventually quit working the little it was. Lithium (1200mg) only worked for about a year. Tegratol (600mg) has worked for me for over 4 years. The thing is you have to take it on schedule everyday and keep a close eye on your liver when you have your blood level taken every month. After trying different medications I am completely satisfied with the outcome of Tegratol so far.