I sell new build so don't get too involved in related sales as we have a company that we out source that to.
You're doing the right thing getting 3 valuations done. Have a chat with them and try and find out how many similar properties they've sold recently ie if they've only sold 2 bed terraces recently and you're in a 4 bed detached then their customer base is probably not right for the type of buyer you're looking for.
Also get them to give you 3 valuations:
2-4 week sale price
6-8 week sale price
recommended asking price.
the 6-8 week price is what you're looking to achieve, but the 2-4 week price is what you'd achieve if you want to move quickly (which I assume you don't want unless you've got your heart set on a property).
Don't just go for the agent who gives you the highest vals, try and chat to them like I said above so that you get a feels of what they are selling at the moment and if it fits in with your property. Not just what they have for sale but what they have actually sold (they can might have a load of similar properties on the mkt but if they haven't actually sold one then bin them).
Once you're decided on an agent and price, keep in touch with them every week for updates. If you've not had any viewings after 4 weeks then something's wrong. Keep reviewing where they are advertising it and the pictures they have on the web etc. If all of that is OK then it's on at the wrong price and you need to discuss that with them.
Don't believe what you read in the newspapers about houses not selling. They are selling so long as they are on at the right price. The main problem with selling at the moment is where people have bought at the peak of the market on a 100% (or even 110%) mortgage and therefore are now in negative equity.
Hope that helps and makes sense......let me know if you need anything else