I bought three, different ones, and someday I may even post the comparison video I started.
In the meantime though, my favorite is
this EZM Electronics Studio GM328. Its the graphical screen variant of the one JoeO linked to above. The firmware seems like a recent version of the open source firmwares with few if any customizations and most/all of the options enabled. As mentioned, it uses a socketed processor, for easy experimentation with different firmwares. I've purchased a few items from the seller and they have always shipped quickly and packed things well.
I also tried a Fish8840 version (red PCB, transformer logo). No telling what version of the firmware it is using, but it is missing a number of features, and also has a design issue that wastes battery.
The final version I tried was from 91Make with Efan modified firmware on a yellow PCB. I thought the graphical display had the best information design, but it also didn't enable some features of the original firmware.
Both of these are mostly SMD components.