I found ELS to be very professional and helpful, we moved into one of their flats over a year ago and have had no problems with their service. We used ELS on a reccomendation from another friend after a bad experience getting a deposit back from a previous agency. They few ocassions when we have had to phone the office they have been very helpful and always phone back (previous review said they store your number and make sure not to answer which is not true). They even helped a friend of mine moving to Edinburgh find a flat before she even moved to the city, they found her a flat within 10 minutes walk of her new job.
I really dont understand the bad reviews, having used 3 different letting agencys in Edinburgh in the past (2Let, DJ Alexander and Murray and Currie) . ELS were miles better on the Customer Service front than these 3.