Well, generally speaking I prefer the forum as well. The problem with SO is that you cannot upload any files, for instance a zip-file of your project which often is needed to get some help. At that point, you need to re-ask the question in the forum and all of sudden there are 2 threads related to your question/problem.
I believe someone just posted that the B4A-forum has now more than 15000 users and this is indeed a proof that Erel has managed to obtain many new users (well deserved). So on the other hand, if we use SO for general and quick questions, B4A will get more known to the developer-community and more users might join the band-wagon. I mean, being present on SO is an excellent way for Erel to promote B4A.
Just my thoughts...