Always try to find an export strength gin if possible - 47.3 rather than the innocuous 37.5 proof - as it makes a significant difference, particularly if you are going for the classic "G & T". Most of the "bog standard" gins are 37.5 proof and IMHO you lose a lot of what gin is all about.
Personally I can't say I'm convinced about the new-ish trend for botanicals from Hendricks, Sipsmith, etc. Give me a good London or Plymouth gin any day. But the botanicals have helped revitalise the market for gin, which is undoubtably a good thing.
If forced to choose I would normally go for Tanqueray, but I have a bottle of unopened Crown Jewel (Beefeater 50 proof) that I am saving for a special occasion!
If making fruit gins then I buy own-brands from the supermarket. That said, both Tesco and Waitrose do some pretty good own brand gin - Tesco currently do a 43 proof London gin that is really very nice.
willie_gunn