About to start meds. Prescribed Depakote. Any other suggestions?

My son had his first seizure at 15 in 2010, then 3 years later at 18 in 2013.  All tests (EEG, contrasting MRI, etc.) were negative.   We chose not to medicate and our doctor concurred.  Our son now 20, had one this year in June of 2014, which was 14 months after the last one.  The EEG showed some abnormality. 

After June's seizure, the doctor prescribed Depakote.   We have not started him on it, awaiting answers from the doctor on (1) why Depakote?   (2) why 500mg (3) is the generic Divalproex okay.   Our next appt is in August where we were planning on getting answers, but our son’s 4th seizure was yesterday, which is accelerating our plans.  

Does anyone have opinions on Depakote vs any other medication for adolescent onset epilepsy before we start?  All seizures were grand mal.