If you have multiboot on your DM500 with a USB stick I would try both images. I cant say which will work best as I have a DM7020.
If you dont have external boot and only use internal flash memory then first make sure that the image was specificly wrote for the DM500 as hardware is different from the DM7020.
Try one image at a time and see which works best, I'd try OpenPli beta first.
Which image is a matter of taste, I've tried, Gemini, Nabilosat, Edg-Nemesis, and like them all, although I stick to Gemini 4.6 and Nabilosat Darstar II the most.