I think it completely depends on the person, how long you have been taking the drug, your unique brain and whether you were mentally addicted or just physically dependent. Personally I find opioid withdrawal a billion times worse than SNRI/SSRI withdrawal, but I believe that is because I wasn't mentally addicted to antidepressants (while I was with opioids) and ADs hadn't been doing much for my depression or anything, so it was mostly weird and scary but not unbearable/painful/making me feel suicidal like opioid withdrawal. With SSNI/SSRI withdrawal I mainly feel very strange, disoriented, get brain zaps, and sometimes feel an erratic or fast heartbeat. With opioid withdrawal I feel like I wish I would die just to stop feeling that way. From opioid withdrawal I get cramps, muscle and bone pain, other pain, extreme sensitivity (even normal things feel painful), chills, goosebumps, sweating, rapid and erratic heartbeat, itchiness, restless leg syndrome, runny nose/teary eyes, yawning, coughing, choking, vomiting, diarrhea, extreme fatigue/weakness, uncomfortable restlessness, dysphoria, intense cravings, anxiety/panic attacks, extreme insomnia, terrible depression, and probably some more things I forgot to list. So yeah, I would take SNRI/SSRI withdrawal over opioid withdrawal any day
But there definitely are some people who find SSNI/SSRI withdrawal even worse than opioid withdrawal, so I guess it really depends on the person and the circumstances.