IMO, depends how much you currently want to spend. Sure, if you have $2k and want hi-cap mags now, go for a used Tromix s12. On the other hand, if you have $600 and want a project for 2012, go for the MKA-1919. Hi cap mags, ect will be avail June sometime. Gives us all a couple months to save money for conversions, although we can buy most parts now if we want.
It basicly goes back to the AK/AR arguement... which reminds me... When will Tony develop an AK gas system for the MKA-1919?