i think rocky is correct...
we know that this reaction goes almost to completion:
H2SO4 + 2H2O--------------> SO42- + 2H3O+
which includes the reactions:
1. H2SO4 + H2O---------> HSO4- + H3O+
2. HSO4- + H2O ---------> SO42- + H3O+
that means in the reaction no. 2, HSO4- must be a stronger acid than H3O+ (a reaction always proceeds in the direction stronger acid ----> weaker acid)