Location and cleanliness are the main things for me, and both were spot-on.
Great restaurants (reccy Hamiltons for modern Scottish cuisine, just round the corner) and shopping right there. Just about an 8 minute walk from George St, 10 min from Princes St. For how close it is to the main areas though, the street itself was quiet and we weren't disturbed at all overnight.
David was very responsive in advance too (I asked for reccys of somewhere to get my husband a kilt jacket), and then Emma while I was there (I couldn't figure out how to switch on the heated towel rail in the bathroom to help dry some clothes overnight).
Very cute and comfortable flat, they had set up the pull-out for my daughter in advance too (other places we were blowing up an airbed, or pulling it out ourselves, which is fine, but nice to have it all ready for her, she felt included). Lovely pub a few doors down that had a local musicians jam session one night which was really fun too.