Truth? My gut 
But after checking it out: Shipyard is waaaaay more lightweight. Most people run open media vault on "light machines" which varies in power, chipset etc.
Panamax solved it via virtual machine, which i think is counter productive (I put a container in a container so you can put a container in your container) at least thats how it feels
GO is a very nice language. Fast, nearly no dependency (compile and run) and easy to maintain (new version? Overwrite all files after compile, done) no relinking, no recompile and giant upload / download.
So in the long run, I would suggest shipyard. Sure it is a risk by betting on GO (developer hype might vanish) so we would be left with a not maintained "product" but I kinda doubt that now. GO seems to grow every day with more "apps" every day.