Blackberry

The thug blackberry is rampant (again) the fruit is plentiful but very sour unless picked when quite mushy and ripe, not something you'd scrump because you end up covered in blackberry juice stains. The fruit is very seedy, so much so that P prefers the blackberries be turned into a smooth sieved couli - he might not be so fussy if he had to process and sieve the stuff himself. I'm thinking of replacing thug with a friendlier, sweeter variety, so I'm researching blackberry varieties . Some say the thornless ones don't have as good a flavour as the prickly ones. Anyone got any advice?