I have tried both Taliskers, though only have notes on the 25yo at hand. Reading these, it was a bit of what you would expect from a Talisker, spices, plenty of pepper and cough syrup but with more of a sweetness. On the nose a mixed bag from butchers shop to dried cereals to the harbour side. Overall it was quite raw and the alcohol screams out!
The 20yo If i remember was from refill sherry casks. I tried this in a blind tasting and thought highly of it. I find Talisker a difficult malt to gauge, especially at older ages as there is not much out there. Some OMC bottles under the name Tactical which might reach the US. I think if given the choice I would go for the 20yo.
However, and I know its Talisker you are asking about, but, the Caol Ila 25yo bottled 2004 was a stunner. If your store stocks this then it would beat the Taliskers hands-down, IMHO. I am sure you will get more postings to help you decide here though.