When it come to a surprise spin attack it is definitely Pakistan since they have all spin options. They have an off-spinner who has immense Doosra, Hafeez who can quickly eat overs without going for plenty, Afridi has a superb faster one, Abdur Rehman is a very good left arm spinner and he showed his worth in tests against NZ plus he too is very tidy when it comes to giving away easy runs.
But on papers Srilanka has the best spin attack with Murli and Mendis as thier trump cards. Second Should be India but they have too many part time spinner who can go for plenty on any day but they are very handy against those teams who can not play spin well.