Glasgow. Studied there for three years, lived there for nine, and I have a friend who moved to Aberdeen after h graduated so I know what it's like. Aberdeen has a terrible nightlife, costs a bomb, has little to do otherwise and is horribly isolated from the rest of Scotland.
Glasgow has the best nightlife and live music scene outside of London IMO, phenomenal architecture (from the city centre gridiron to the West End tenements to the museums and galleries), and is an hour and a half by train from Dundee, Edinburgh and Carlisle.
And the law school at Glasgow Uni is very well regarded.
I literally cannot think of a reason to study in Aberdeen instead of Glasgow.