I keep track on my own of which competitions I believe to be the best & worst based on the experiences of mine and my friends. However, I am not aware of any online reviews. I would think publishing such a thing would not be very kind, given that many/most competitions are not out to make much if any profit, and that different volunteers with different qualifications are involved from year to year. It's true that competitions can be a crapshoot, and that any given comp can be good one year and bad the next. This exact topic is part of the reason why I no longer enter very many competitions anymore (there are many other reasons also that I won't get into here, besides the obvious: "laziness"!).
While I do think there is *some* consistency in performance at the same place, same people, same time, etc., I also know for a fact there can be a LOT of changes and variability from time to time, much like the stock market where it is often said "past performance is no guarantee of future performance" or words to that effect. I'm also aware of at least one or two examples of competitions where after several years, the club apparently had finally gone through enough grief that they replaced the organizer and basically started over from scratch, but still same place, same time, same name of the competition. I'm sure there are other similar examples out there all over the place.
So no, I don't know if you can or should find such reviews, nor should you necessarily even base entrance to a comp on such reviews. Understand first and foremost that competitions are ALWAYS a crapshoot, then knowing that key fact, choose whether or not you want to enter anyway. Maybe you do, maybe you don't. And/or, keep track on your own. That's what I do. That's the more polite thing to do, I think. I'm not going to badmouth publicly any competition where I think the judges suck every year. I *know* this *does* happen. But I'm not going to shame them publicly. Sometimes a judge just has a bad day, too. We're not perfect machines. We're humans, and we have subjectivity and bias and all that. Never going to be perfect, nor even consistently pretty great or whatever. If you find a comp you don't like, don't enter it anymore. Find another one. There are HUNDREDS of comps you can enter if you don't mind shipping.
I feel like I'm rambling so I'll stop here. Cheers and good luck.