It can be frustrating, there are so many options out there now. Literally hundreds of answering services to choose from. I think it largely depends on what you want from the answering service - do you need a full time service, out of hours, does it need to be 24hr, pay as you go, long term contract, based in a certain area?? These are all questions you need to answer and choose a service who can fit your requirements. Not all of them provide a 24hr service, not all allow pay as you go, etc etc.
I can recommend alldayPA. They are a 24 hour service and answer calls 7 days a week, 365 days a year. I think they do pay as you go and long term contracts but I'm not 100% sure. You can read more about their service here. They can also offer a virtual receptionist service (i haven't used this as I only require phone answering rather than any document typing etc) but here you go: http://www.alldaypa.com/virtual-receptionist
I hope this is of some help! For reviews, once I have a short list of companies I usually just use Google and search for "(company name) reviews" and it should return some results rather than just searching for "answering service reviews". Another trick is to use the discussions search on Google. Search for the company name and click discussions, it usually brings up forum discussions where people are openly discussing the company in question! Helps to see some REAL reviews and thoughts of people who have used the service you are questioning before.