The fees contain 2 separate elements the actual profit costs and the dispersements. Some only quote their profit costs some quote both. Their should be little or no difference between dispersments. So it is the profit costs that will identify the cheeper firm. I would tend to go to a local firm and look for recommendations. An online provider is probably ok as long as things are all in order with title etc and everything goes smoothly. They are geared up to deliver what the customer wants not necessarly what they need. Monitering searches and timeframes is all well and good. But checking title and searches to ensure you are getting what you expected is another. Horror stories include land locked houses where the purchaser has no right of access to their home either to one side or at all, missing info on questionnaire s, uncleared charges on the land or neighbours who have a right of access over the patio. I have come accross all these before I got bored with Conveyancing.
If you a buying a fairly new build house that has changed hands a couple of times then I would be happy using the cheapest and most convenient. An older or rural property then I would use a well regarded high street Solicitors in the area where I was purchasing.