I've lost my original firmware (OpenDingux) due to my own stupidity when I received my LDK. So not really sure now. Do you still have LDK's original firmware? If it's not too bothersome, please upload it somewhere.
As for the thread, I'm currently using "Useless Firmware" which was said to be older and outdated than RetroFW. But it works good for me, and it got more games in it, so I stick with it. And seems to be "closer" to OpenDingux.
I did tried both, and by far I don't see any significant difference in terms of emulation performance. But I didn't do any intensive test or benchmarking for that matter too, so i don't have any data to back it up. I bought LDK for playing games, not to benchmark it.
As for which one is "better", well seems that the key persons here suggested RetroFW. Useless is not developed anymore. Also more games are ported gradually. But everything happens under the hood, the users won't see much difference.
I suppose it will help the development if more people are using RetroFW, and promote it everywhere.
Check out the stickies, RetroFW even got couple of new menus and skins.
But for me, I'm good. Untill ROTT, Falling Time, and proper Wolfenstein 3D ported to RetroFW, I'm sticking to Useless.