There has been much written about both of these gliders. If you use the search feature you'll hear this:
The 4 is arguably the best handling glider ever made with good performance. The 3/3a is perhaps an under rated value in the market. In strong conditions the 3/3a will go faster, otherwise the performance difference isn't worth chasing. Consider the trailer condition, aircraft condition and location in your interest level. The 3 has heavier wings, the 3a had slightly lower performance than the 3. Flaps on a first glider might be an unnecessary burden depending on your experience and skill level. If taken care of the finishes last 15-20 years it seems. Sanding and polishing will extend the life but many of the gliders from the 80's on are hurting right now. A refinish costs about as much as these airframes and there are only a handful of shops in the US that know what they are doing.
I say buy the nicest thing in your price range and find a reason to love it.. I never wanted an ASW-24, but guess what I'm flying these days?
Good luck and enjoy the hunt!
-Doug