I have a few comments having sold most of the machines here.
The Gerber Ion as a slow machine...it is quite good with through put compared to others, not as much taping and fiddling to get a sign onto and off the machine. People who use flatbeds learn that the print time is not the only "speed factor" I have seen many who have found unique niches as far as getting the Ion ink to adhere to some very creative applications. Tech issues, yes the techs do not get to just walk away from this machine and I would budget in a service contract, but I would on any machine. I have not seen the fading issue myself.
The Agfa, nice machine, not true flatbed but this does not hold it back much. Nice quality, can't say much bad here, adhesion is second to the Ion but pretty good even on coro.
Oce/Fuji nicest machine of the bunch IF they could get adhesion issues sorted out. If you print lots of coroplast, think hard. Also it does take a bit more taping and covering of the unused vacuum holes which affects throughput.
HP950-Very close competitor to the Agfa. Nice machine, very high quality. I have not seen long term results yet or a lot of adhesion testing, my experience with this one is slim.
Mimaki- Very capable, diverse machine able to do things the others can't. Expect to be your own technician and very frustrated at times. I like what it does, just don't like how often it frustrates.
The others well...they can be priced right...
I think I might have a used Agfa available if you are interested. What RIP software are you currently using, the other consideration is that some may have a shorter learning curve as they might use software you are already accustomed to.
Craig