Buying LS3a or ASW20a? ~$25k cross country glider. Which one and why?

The original LS3 have the reputation of a slightly better performance than the LS3a. The LS3 polar measured by idaflieg is about equal to an ASW20. There were several sets of wing molds being used, perhaps one of them was less accurate. This info comes from the LS-book which has been publishes a few years ago.

LS3 are quite heavy, in the 290-300kg region. But that's not a big problem if it comes with a good trailer. 3a have about 20-30kg less weight. This difference in weight comes from split flaperons without lead ballast and a different construction of the wing spar. The spar caps on the 3a are directly under the wings outer laminate which allowed lighter spar caps being used. In the LS3, the spar caps are under the foam sandwich laminate. That requires more material in the caps to be used for the same strength, but prevents any warpage to show in the wing surface.

The LS3 fuselage is structurally very similar to an LS1-f whereas the LS4 more ore less took over the fuselage from the LS3a with the new empennage. For that reason an original LS3 (non -a) cannot be modified with an integral tail wheel.