Currently, the Peace Silver Dollar, is the best 90% silver dollar buy. Unlike the Morgan Dollar at $30+, you can still obtain common date Peace Dollars for under $30 and get better deals buying in rolls or bulk. However, the mint marked and mint state grade Peace have gained ground on the Morgan.
A few facts lead to this up-swing in premium: Peace Dollars were once not very collectible and because of the high mintages of the 1922, 1923, 1924, 1925, they where regarded as the lesser of the two major silver dollars of their time. Recently, last 10 years or so, collectors have come to appreciate the Peace more, and realize how low some of the S and D mint marks actually are.
In addition, some of these mintages are much lower than the Morgan Dollars, and MS65 Peace Dollars are more difficult to obtain than their Morgan counterparts.
It use to be that everyone hoarded and desired the 1921 and 1928 Peace, but from the list above, you can see that's not so much the case. Of all the dates that are breaking records in high grades, not all of them have been dated 1928, 21 or even 34-S as some might think. Below I have an image of this beautiful 1925 MS68 Peace Dollar, courtesy Heritage Coin Auctions, and you can click on the coin to see a larger image.