From my opinion Methadone is the worst withdrawal ever, it takes a long to time to show up and last for a fuckin long time.
My first experience of withdrawal was after 2 years of slowly using codeine/opium once in a while to snort/smoke a little less tha a couple of g's of H a day. At the time I was in london and was scoring some decent white powder from a turkish guy. My gf and I were planning a trip in asia before heading to OZ for a year, I thought It was the best moment to stop using, at this periode I was working a lot, having a job in a nightclub until late so I was using uppers to stay up (mostly bad cocaine and amphetamines) and using H to come down and sleep, as well as during the day to have a nice buzz I was still enjoying it even if I knew that I would start to feel shaky and sweaty after a da without I never experienced a full on WD.
So we took the plane, I brought couple of grams with me and had the best plane ride ever, snorting line every now and then and nodding hard, scaling bloody mary in between, the first was also awesome, wondering around Bangkok buzzing hard. Then the dope was gone and I was waiting to see what would happen, and boy, it hits me fuckin hard.
I started with the shack, chill and diareah and nausea. After 48 hours it was fuckin insane, I was sweating balls, having my whole body into spasm of muscle contractions, the next step to restless syndrome, for 2 or 3 hours at the time, this state lasted 3 day, the 4rth day I started to feel better, i couldn't sleep more than 20/30 minutes at the time but my mental state wasn't as bad as I expected. I think that the fact we had a lot to see and discover helped a lot. I started feeling better after 10 days.
The last time I stopped at 60mg without tappering, I was given Valium and some muscle relaxant but it didn't help much, it was 10 days of pure madness, restless legs, being cold constantly, chills, diareah 20 time a day, permantly feeling like puking and horrible mental state for month after. After these 10 days where I have slept 20/30 minute a night, taking 6/8/9 warm bath a day I was left with a depressive state that I never experienced before. One day I lost it like it never happened before, I was into some weird delirium, having visual and auditory hallucination so bad that I had to the ER, they put me to sleep and I walk up the next day feeling like shit.
I talked to the doc and he told me that maybe the lack of sleep and the residual effect of withdrawal trigger the mental state. He was nice tho and told me that I should be proud to go through all this to get clean and that I did well to come before it turns bad.
I felt it would never end, my whole body and mind was up side down.
Then for 3/4 weeks I would cry few hours a day, even I did felt specialy sad for a reason It would just come like that without warning or I would be all euphoric almost feeling I took some drugs then back to sad and disoriented again.
I also felt totaly empty of all force for about 6 month not being back to normal, I still feel today that this withdrawal left some scars, since I don't the same anymore. Anyway after 7 month low I decided to go back to methadone at a low dose and tapper slowly because I couldn't handle it anymore, and god almost instantly I felt alive again. My gf at the time after seeing me like this told me that staying clean was certainly a good thing but living in such a state wasn't looking really human thing to do, I felt some relieve to ear that from her.
So far the heroin WD is for me more intense but shorter compare to methadone. The day I will have to go through it i'll taper slowly and try to switch opiate, for example methadone, then morphine then codeine. I'm sure it will be less painfull.