I would always say use an agent. If you shop around you can get a fee from 10% to around 20%. Try and knock them down to 9% if you can, say it's not worth your while otherwise. They desperately need your business at the moment since houses aren't selling, so rentals keep them going.
By using an estate agent you save all the day to day hassle of tenants problems and potential issues of non-payment. Some estate agents will give you a 12 month rent guarantee, and most will get you references and a guarantor so your house is safe and the rent is paid. They also know what to do re. legal stuff if there is a problem and you need to evict the tenants.
Work out your mortgage and add 10% (fee) on top. That is what you would need to charge in rent. Is that competitive with the locality and other similar houses in the area? If not, it won't rent! Remember you will also be paying buildings insurance every month and you will have to insure the basic contents if there are any- curtains, carpets etc, unless the deposit covers these.
If you advertise your house yourself on the internet or by making posters etc and sending them to large businesses or schools to put on their staff room board, you can do the viewings yourself and then send the interested party to the estate agent to do the legal stuff. This way you save paying the estate agent the fee for finding a tenant, as you have done that yourself!
I'm in the process of renting mine out at the moment, in order to move into a smaller rented place.You can also go with more than one estate agent if you like but do read the small print on the contract they give you. It is usually no let, no fee, and sometimes they may want to be the sole agent for the first 4 weeks.
Good luck!