I got my De Kerf stove enameled a few years back. The Argos blokey (incidentally, highly recommend using him) said that enameling looked better with a bigger choice of colours, but powdercoating lasted longer. Since I wanted something close to the original ‘petrol’ colour (Some say green, others say blue) I went for the enamel. It’s not that tough, so I’ll be going for powder next time. After about three years (one of very hard use) there are some scratches in the paint, none through to the metal. However, chainsuck did wear through to the chainstay, but was easily resealed with clear enamel and then touched back up later on.
I’d suggest a good powder coat – sounds like getting the right paint shop is at least as important as the finish you choose.