Basically... It's much of a muchness. Yes, an LCY arrival is more convenient, but go for what suits you best in terms of both timing and cost.

Liquids are still subject to the 100ml rule, as elsewhere, so you wouldn't be able to bring anything other than miniatures in your hand luggage. Not that you'll necessarily be more able to buy decent whisky at a decent price in Edinburgh compared to London (or indeed Heathrow duty free on your way home...)