main is the state with the fewest quarters issued.. so in theory, they should be the most valuable in time..

but so many people are making sets of the quarters, (or as least started to make sets) i suspect the last quarters issued are the one least likely to be 'collected' when current, and will be the 'rarest' 50 years hence.

i don't think a full set of all 50 state quarters will be worth much (more than face value) in my lifetime... of course, i could be wrong and live to be a 150 years old...