In terms of most up to date image it's OpenPLI which gets nightly builds also very stable and has a built in downlaods server from which you can download the cams you need and other plugins. Also supports Rytec XMLtv EPG. The Maxvar version is prefrable for a DM500 because it's lighweight minus all the un-needed bloatware.
Commando is also very good, good built in EPG, and runs light. If you have clone DM500 unuts, avoid any recent Gemini images they contain clone killer code which will overwrite your bootlaoder and brick your box...then you'll ned a JTAG to recover it.