Sansbury:- Still quite good, not as good as Safeways. tend to be a bit soft and go stale very quickly, must be eaten as soon as perchased. Look out for the custard ones and blackcurrent ones.
Asda:- there is great variation between stores and batches with Asda donuts, sometimes they are as the safeways sometimes they are terible. stick with the plain old ring here.
Tesco:- despite being the biggest supermarket chain in the UK, Tescos donuts (and bread/confectionary in general) is by far the worst. The best thing about Tesco donuts is that you can get 10 mini donuts for 99p (ok the're about the same price as the others but I had to say something positve) try to avoid tesco donuts unless completly imposible.