Take this with a large grain of salt, as this info doesn’t come from first hand experience but rather 2 local printers close to me, one of whom I consider a good friend (and he taught me a lot of what I know). But so far the results on the all-metal hot ends that I’ve been subjected to is as such:
MetalMagma hot end from http://trinitylabs.com/ – Nothing but trouble. While there is a chance that this just happened to be from a badly machined batch, it was constantly jamming. Likely due to heat creeping up the nozzle. This was also tested by Chris. He attempted quite a lot to resolve the jamming issues, fans etc.
Prusa Nozzle from RepRapDiscount.com/Josef Prusa – The user that attempted using these is somewhat of a novice, but largely experienced the same thing. Heat would creep up the nozzle and eventually jam. Also only comes in 3mm, no 1.75mm version available.