I buy Boots own brand ones simply because I can buy more in one go than I can in any supermarket due the the pharmacist being there.
As far as I'm aware, aspirin is aspirin is aspirin.
The only conceivable difference between aspirin tablets is if they have an enteric coating - this protects the stomach but, ironically, delays the effect of the aspirin.
Enteric coated aspirin is a 'premium product' and will be more expensive everywhere.