Muggz...price, availability, driving style, different compounds..etc etc...the list goes on. To give you an idea of who's using/used what...

Dunlop....Lister, Austin, Dunkerton, Herridge (jnr)
Toyo...Lister, Cerro...+...
Bridgestone...Austin, Pummer, Pollard, Paris, Lloyd
Silverstone...Herridge, Pummer, Dunkerton
Continental...Hoare, Healy

Not sure what others use (eg Alex)

Good luck