This time it's a 4-way comparison between Beefeater, Tanqueray, Sipsmith and Aldi's own-brand 'Oliver Cromwell' Dry London Gin.
Method
Round 1: Made 4 G&Ts using 25ml of gin, 75ml of tonic, ½ a slice of lime (partially squeezed) and approximately equal amounts of ice. Labelled each cup. Then got a third party to re-label each cup and erase original label, noting correspondence. Comparative taste-test (invited housemates to sample drinks as well).
Round 2: Re-filled cups with 25ml of gin and only 50ml of tonic. Entirely subjective taste-test.
Notes
By the time the process of obfuscation was complete, a significant amount of the ice had melted, making the drinks very weak. Probably should have used less tonic to begin with; a 2:1 or even 1:1 ratio might well have been more useful for this test.
Round 2 abandoned all pretence of scientific rigour. This was probably for the best.
Results
Round 1: Drink C has slightly more depth of flavour than the other three, which are virtually indistinguishable. Other drinkers show slight preference for drink A relative to B & D, but this is only slight. (C is revealed to be Sipsmith, A to be Tanqueray).
Round 2: Despite popular opinion favouring Tanqueray as the best sub-£20 gin, I personally prefer Beefeater. Nonetheless there still isn't much to choose between Beefeater, Tanqueray and Aldi's own-brand. Sipsmith, meanwhile, is way ahead of the rest, with far more depth and complexity of flavour than any of the others.
Conclusions
The bottle of Beefeater that I already have is probably enough to last me until the weather turns and I stop drinking G&T, especially since I am also enjoying a variety of other summery drinks such as mojitos, rum bucks, etc. When I eventually find myself needing more gin, Beefeater would be a solid choice with which to re-stock but considering the very small difference given the price, Aldi's own-brand would seem the more economical option. That said, the noticeably superior Sipsmith does justify the step-up in price so trying other more premium/craft gins might well be worth the extra expenditure.