If we are talking about over the last 20-30+ years or so. Pakistan easily takes this one. Abdul Qadir, Saqlain Mustaq, Mushtaq Ahmed and now Saed Ajmal. Even Afridi has turned his bowling around completely. Heck even Kaneria was a good spinner before he started cheating, or maybe he was cheating all along who knows.
"I was the happiest man in the world, happier than Bill Gates"- Tamim Iqbal