I said oxymorphone because i have had the most withdrawals from it, but i would imagine heroin could be even worse if you were doing a lot everyday. It's hard to say which is worse, opiate or benzo withdrawal. I guess it really depends on the amount of benzos, and strength, and how long you've been on them, same thing for opiates. benzos have less physical symptoms than opiates, but usually people coming off of high doses of xanax, rohypnol, and/or halcion, would need a very slow and long taper to help be comfortable, otherwise you will have a withdrawal that lasts much longer than opiates, usually a lot of twitching, possible seizures, and a lot of extreme psychological anxiety. It's rare, but it is possible to die from benzodiazepine withdrawal, so if you have a seizure or you're experiencing a lot of twitching or convulsions, get yourself to the ER. It happened to me once, and they had to give me a triple dose of IV valium....I don't know what in a hospital how many mgs 1 "dose" is so I don't know how much he gave me, just that it was so nice for the convulsions to stop and feel ok; so, i would say that benzodiazepines have the potential to be the worst to withdraw from. I don't know a lot about barbiturates since they aren't normally prescribed anymore, aside from phenobarbital occasionally, which has a 2-7 day half-life, but I imagine the withdrawal symptoms from say secobarbital or pentobarbital wouldn't be very pleasant either.