I was very impressed by eMoov: they were polite, helpful and friendly throughout. There's no question in my mind that I will use them again next time around. I chose them because they cost so much less, expecting I might get a little less service for my money but I found that wasn't really the case. They also provided much more realistic and useful advice on pricing than any of the supposedly knowledgeable local highstreet agents did.
I paid monthly at just under £120 a month (including VAT), which ended up saving me £1600 compared to the highstreet agents. They even provided the EPC was provided as part of this cost and they sent someone round to do the EPC, take photos and prepare floorplans within a few days. The cost is paid up-front regardless of whether they found me buyer. Some may see as a disadvantage but I think represents a fairer and more transparent business model, since with a traditional agent you're effectively paying for all the times they failed to sell other people's houses.
They don't do viewings, but I prefer do them myself anyway and when viewing I prefer being shown round by the owner anyway since they can answer your questions better and have a better knowledge of the property.