Personally, I will be sticking to MC 11.1 for now.
MC 12 looks very promising (I love the new theme, tagging is better, and video playback is more user friendly), but when I tried it - it hogged much more of my CPU than MC 11.1.
To be fair, MC12 is still in beta, and the MC team is very good/fast at fixing bugs/errors.
Again, MC 11.1 does everything I need for now. If I notice MC 12 is doing more stuff that I could use, I will upgrade (video conversion, easier music transfers/with rockbox, more user friendly – I do not even think I half of the features in 11.1). But for now I am going to hold on to my money, until I see more development in MC 12 or possibly even MC 13.
Furthermore, I agree with the above… MC has been the best so far in terms of stability and speed with large media collections. I believe the developers and users are more technically involved and thus can appreciate the software more than an average user. I also do believe that with the recent changes in MC 12, this gap is narrowing. I am looking forward to see what the MC crew has in store for us!