How many games are played on GCCG now?
I definitely prefer Gemp, as playing there is way faster (maybe because I never became very familiar with GCCG interface, as my account became corrupted, crashing the server each time I logged in, and I didn't start another one). Best thing in Gemp is that it's still in development, so even if it's missing some features, chances are they may be added in the future. I would not rush with closing down GCCG, but at some point in the future it might become redundant.
A thing that would IMO be the best to happen is if, together with MarcinS, you find a way to merge Gemp with TLHH, so that there's common login/password and both sites are crosslinked whenever it's useful. This way Gemp would gain forum (which it IMO needs) while TLHH would gain a way to play which is "right here" and doesn't need any additional downloads or registering anywhere. I feel this would be the best thing possible - forum with its archive + playing environment + detailed database about the game, everything in one place, is best way to gain players (BTW: there are people playing on Gemp who have never played LotR before, so I think it is possible to attract new people to the game, which is what we need to keep it alive).