Ron Guth:
The 1910-S Dime is generally perceived to be the rarest of the three mintmarked 1910 Dimes. It certainly has the lowest mintage. However, in terms of the total number of survivors that have been certified by PCGS, it is the second rarest after the 1910-D -- and it is not even close. In Mint State, the 1910-D and 1910-S are almost on par and, in fact, there are more nice 1910-S Dimes than there are 1910-D's, especially in MS65 and better grades. The 1910-S tops out at MS67, where there are a couple of examples with stunning color and eye appeal.
The luster on the 1910-S ranges from frosty to brilliant, with a couple of Prooflike early strikes known to exist.