Well lets say that I think a lot of us suffer from a significant amount of parental guilt over childcare, and I tend to find that nursery users are often in some state of denial - typically because if you work certain hours etc there are often few affordable alternatives. It is so difficult to find a really fabulous nursery ime, and if you do I would be surprised that it has spaces. I found one that was superb but had an 18 month waiting list unless you were a single parent.
Sorry that is a slightly depressing and unhelpful statement. I think that you may get more honest assessments from parents once their child has left, especially once they are in reception year as there can be comparisons with other nurseries. Certainly looking at the reception class at the dcs school you could tell that one nursery stood out head and shoulders above the rest in terms of preparing the children for school (and I'm thinking of all aspects of readiness here).
No idea of your family demographics but if you have an idea of the primary school that you'll be going to you may find that asking their opinion could be helpful?