I have used bridgestones, yokohama's, pirelli's and Toyo's on GS's and have driven over 170,000 miles.
Bridgestones, OK
Yokoama, Poor grip, wear out quickly
Pirelli, poor wet weather grip and expensive.
Toyo, excellent grip, good wear, very good price
My vote goes to the Toyo's, I have just removed bridgestones from my TVR and replaced then with Toyos as TVR now fit them as standard.
Also
Pirelli P6000 £108.30 each
Yokohama A411 £115.70 each
Toyo Proxes £57.40 each ;)
There is just no contest in my opinion....... :D