The withdrawal from Ultram (tramadol), when taken in excessive amounts over time, is worse than any of the other opiates (possibly with the exception of methadone being worse). Tramadol not only causes a synthetic opiate withdrawal syndrome, but it also affects the GABA system, serotonin, and possibly others.
It's like going through opiate withdrawal, benzodiazepine withdrawal, and SSRI withdrawal all at the same time. The other interesting thing about tramadol is most people can consume a ton of it without throwing up or overdosing. Extremely high levels of tolerability can occur -- unlike most of the other opiates. (The others would kill you before such a level of tolerance was reached).
Having said all that, tramadol is probably easier to wean down the dose than any of the other opiates. As long as the user has enough supply to cut the dose over a period of 2 to 4 weeks, the withdrawal will be far less problematic than the others. It seems to have more gradual mental effects during the weaning down process. Tramadol also has a delayed opiate onset, so the opiate craving is far less when weaning down. In fact, some have found it useful when withdrawaling from harder opiates. However, immediate substitution of tramadol may be problematic because it can block the effects of some other opiates.
Nevertheless, heavy alcohol withdrawal tops them all, and is probably more deadly than any of the opiates over the long term. If you really want to test the limits of withdrawal hell, drink all day and all night for a few months and then quit suddenly. Drink about a liter (quart) or more of hard liquor every day for a year, and then quit abruptly!!! If you live to tell about it, it will make the opiate withdrawals seem like "mild complaining".