You shouldn't go could turkey on anything. With alcohol you should take benzos, with opiate WD take anything that helps you feel better, studies says GHB, gabapentin and lyrica are very good for opiate WD. But up to you if you want torture yourself.
Having something to ease withdrawals isn't *always* an option. Besides, my benzo dependency renders them borderline useless to help in opiate w/ds. Also my metabolism causes me to get precipitated withdrawals from suboxone up to 48 hrs after my last dose of even a short acting opioid (like morphine, heroin or oxy). Haven't tried the neuroleptics (pregabalin & gabapentin), nor have I tried clonidine. They're supposed to help too. But I usually make do with my regular dose of bromazepam (no extras during opi w/d except sometimes I'll use a higher dose ONCE, and only for extreme cases of insomnia).
Anyway, for alcohol it is litterally necessary to have something to taper down with (benzos preferably) if the habit is big enough, since going C/T off of alcohol is quite dangerous.
But for opiates it's not strictly necessary, as it isn't dangerous to go c/t. It sure is easier when you have some stuff to help of course, but opiate addicts don't always prepare for withdrawal (well, that's my experience anyway) since they know it's not actually dangerous no matter how shitty they will feel.
On the other hand, I've never let myself run 100% out of benzos, since kicking those c/t could lead to seizures and other nasty & dangerous stuff. I think that's big part of the reason that I always make sure I don't run out of benzos early (and am able to do so quite easily). On the other hand I don't get much out of benzos recreational-wise, so there is never really any temptation to exceed my dose unless I desperatey wanna knock myself out because of insmnia.
Anyway, ON-Topic: I think alcohol w/ds are probably the worst, but I can only speculate as I've only gone through hardcore opiate and hardcore benzo w/d. While benzo w/d (imo) isn't as bad as opiate withdrawal (in intensity), the long duration of benzo w/d more than makes up for the lesser intensity compared to opiate withdrawals. And as I understand it, alcohol w/d is a LOT more intense than benzo withdrawal (similar, yet a lot more 'intense'), ergo a lot more dangerous to do (without proper medication anyway). And seeing as benzo withdrawal is already that bad, I'd guess alcohol withdrawal is the worst. Though the duration is closer to that of opiate w/d's than it is to the duration of benzo w/d's. (Around a week if I'm not mistaken, though I'm not 100% sure about this)..
TL;DR - So, I'd say alcohol is the worst (I think), haven't experienced that one myself but from what I gather it seems rather horrific. Don't get me wrong, opiate withdrawal (from a large habit anyway) SUCKS. Only I think alcohol withdrawal sucks more, with the impossibly strong tremors, chance of deliriums, seizure risk and all that other goodness... Although, I've seen pretty bad alcohol addicts go through alcohol withdrawal close to symptom-free because they used benzos (most drs give it to alcohol addicts who want to quit for a semi-quick taper & rehabs use it too for the exact same reason - and when benzos are used, the patients seem rather comfortable whilst getting off alcohol - so detoxing from alcohol with professional help does not seem THAT extremely hard). For opiates the only options remain methadone & suboxone. Suboxone doesn't kill all my symptoms, and methadone has a terrible w/d of its own. So maybe, if you consider the meds available to help with detoxing, opiates are the worst after all.
It's really hard to decide.. Lol.