I agree with the previous post, Elite and McKenzies are the one to go for in Manchester. I would consider Bondgirls if you want save money as some girls offer the 30min option.
The general problem with agencies is that you do not know what services are on offer by the girl until you are there and played, I found myself paying some expensive price for some very basic service, quite annoying. In this McKenzies stand out as some off the girls list the likes. Also the option of trying the girl first for only for 30min could help to avoid big disappointment.