Someone asked about the speed. I measured with the Minimig AGA "newcpu" core 1.0,with SysInfo : CPU speed was on par with a 65 MHz 68030. (although the emulated CPU is a 020). It's better than what I had back in the days so I'm happy
The readme of version 1.1 says CPU speed was reduced a little bit to increase stability / compatibility, but I guess there is still room for improvements as there was a HUGE increase between the previous beta and version 1.0.
The current problem is compatibility. Former ECS core was close to 100% compatible. The current AGA one has issues at the moment but it's very recent (first public version at the end of june). Actually, quite a few AGA games have graphical glitches, and some require the "Turbo chipset" mode to be fullspeed, which reduces ECS compatiblity. Temporary workaround, but I'm quite confident
That's why I disable the TURBO mode most of the time. I can play my favorite AGA games perfectly : Slam Tilt and Roadkill !
As for the MiST vs FPGAArcade. From a user point of view, they are not so different for the time being. The MiST has more cores and features from a software point a view for the time being, probably because the it is way cheaper and more widely available. From a hardware point of view, the FPGAArcade is supposed to be much better though (larger & faster FPGA, better audio converter, future 060 daughterboard support, DVI output...). However, the MiST has some cool stuff built-in (4 USB, 2 MIDI ports, USB power input).
Also, it's important to note that the cores developements are separate. The MiST Amiga core is built upon the Minimig one and the FPGAArcade seems to follow its own route. Same for the Atari ST core. There is cooperation regarding the TG68 (68k emulation), though.
In the long run, we can expect great stuff like Ethernet, RTG and AHI support. If those meet enough success and maybe if other developers jump in I guess