Opinion Polls can be found at Anarchy tourist sites, I've collected over 10 of them while doing exclusively Anarchy. But, as others have said, OPs may be more rare at Anarchies due to SCPs also being there in copious amounts. However, personally I still stuck to Anarchies because it's more fun for me to murder everyone (and not bother with notoriety) than hide and risk triggering alarms. At the end of the day it's a gameplay loop and you have to find a way to make it at least minimally engaging for yourself. So if you enjoy "Thief"-like stealth gameplay, then go to non-Anarchies, if you're more a shoot-em up kind of guy, then maybe you'll have more fun in Anarchies, even if it takes longer.
One other thing to bear in mind is the "dry spells", when OPs won't drop for a long time without any discernible reason. People had "dry spells" for as long as a dozen consecutive raids, with OPs appearing in drops afterwards. If you're in a "dry spell", the options are to stick it out and hope for OPs to reappear, or to change location. Neither guarantees anything, it's a roulette.