Best student satisfaction? Best quality of teaching? Best accommodation? Best location? Best sports facilities? Best social life? Best graduate salaries? Highest ranking in league tables (which combine a variety of different factors)? Lowest drop-out rate? Most degrees at 2:1 or above? Something else?
For, quality of teaching, I'd say Strathclyde wins, but Heriot-Watt isn't far behind. That's according to the National Students Survey (as published by The Uni Guide):
For league tables, The Complete University Guide (for Economics) has Strathclyde and Heriot-Watt effectively tied, with Dundee somewhat behind.
The Guardian has Heriot-Watt and Strathclyde towards the top of their table, and Dundee towards the bottom.
Note that league tables are often a poor way of judging universities, as the criteria used to form the tables, and the weightings used, may not align with what you feel is important.
For nightlife, sorry I haven't a clue. Logic would suggest that, location-wise, Heriot-Watt and Strathclyde would be better than Dundee. But I don't know if that's true in reality.
With Heriot Watt university being on the outskirts of Edinburgh. So for nightlife for Heriot Watt you'll be best going into the city centre of Edinburgh where there's hundreds of pub's, clubs and restaurants you can go to. You'll certainly find it busy especially at weekends when students are mainly going out for a good night out with friends etc. I found Edinburgh good for night's out when I was studying there as I'm not from Edinburgh as Glasgow is my home city as back there working now I have completed my degree few years ago.
Strathclyde university is in the heart of Glasgow city centre - you are a throwstone away from a very busy city centre nightlife and daylife as it's as busy during the day. Plenty of pubs and restaurants and clubs in and around the city centre for you to go to.
Also remember that depending where you live about in both Glasgow and Edinburgh you may have to travel in but good bus service in Edinburgh and Glasgow as well and also there's the subway you can use in Glasgow as it brings you into the city centre at two stations ( this is depending on what end of the city centre you want to go to).
Person in post #6 gave you the league tables for each university as I couldn't tell you this.