While TSF may be more active recently, it is 1.23 that has always had the most skilled players around (imo), who are not as active or are not active at all. Personally I use both jj2 versions. You can easily join a server that of another version by using a version editor as stated some posts above. TSF players can always play in 1.23 servers, but 1.23 users can't always join 1.24 servers due to some compatibility issues. Some recent servers will allow both versions to join.