Just got back from a day trip to Edinburgh.
It's a reasonable day trip. OK, I had to get up a little earlier than normal to get to Stansted Airport, but not too much earlier and some of that was just in case of traffic problems.
Flew with easyJet. Now, last time I flew easyJet they marooned me in Glasgow late one Saturday night (although this wasn't so bad as I have relatives not far from the airport that I managed to see as a result), but this trip was pretty good - both ways on time, decent flights, and everything worked out fine.