Well, after some (great!) on-and-off development, sadly the devs seemed to have favored the greater userbase of the PSP, despite its screen and joystick. If some of the devs had liked their GP2x and kept at it, Amiga emus on GP2x had been much better off. But they were few, so there seem none left.
I offered to code on some parts, but the project was handed to another dev and I got no response. AFAIK (haven't checked #gp2xdev in a while), noone works on either of the emus anymore.
The big issue is that enough time hasn't been spent on making various standard trackloaders work properly.
Apart from that, the Amiga custom chip timings are much harder than most (all?) other platforms to emulate. But the big problem is the "cracktro loads with trackdisk device, click mouse and game trackloader fails to load game". :P
I'm sure you've read about different "cpu-chip bias settings", and for quite a few games there is a cracked disk image that works.
One way to work around it could be to implement a harddisk unit in the emus, then the HD-installable games should load fine. But the emu must then emulate Workbench etc correctly.
If loaders fail because of the emu code not being able to implement the disk timing fast enough, it might work better on the twice as fast GP2x Wiz. Best thing would be to check if Wiz users have had better luck first, though.
In my experience, even though many Amiga emus are more developed than on the GP2x, nothing comes close to WinUAE. I have to try very hard to make a game fail on it, whereas the others have a substantial failure rate.