It depends on how well the pub keeps it.
Phnuff has two of my top ones with Straw Dog and Golden Jackal - both frequent visitors to my local, which claims to be the best pub in Suffolk for good beer. I don't really care whether or not it's the best: it's darn good in any case.
Adnams Broadside and Explorer are excellent; Woodforde's Wherry is delightful (as are their other various brews). St Peter's are good, too.
The ones I go for most are the local microbrewery ones - the Victoria in Earl Soham has several, all of them delightful.
I find the London ones lacking in finesse, in comparison to the East Anglians. They're also horribly more expensive - which is a bit of a downer, since in my experience you don't buy them, you only rent them (briefly).
Some of the Yorkshire ones aren't bad, either, but the "smooth and creamy" stuff doesn't suit my palate.