Do you know if Realistic Lighting With Customization is one that has problems? That's what I use, but don't have Dawnguard yet. I chose it because it doesn't use any ENB/postprocessing/driver hooking trickery, instead taking the high road of actually adjusting lights in the game. I've been happy with it. However, for some reason the author has chosen to block comments on the Nexus until the next version is out, so if anyone is having problems with Dawnguard it would be hard to tell. The next version looks incredibly ambitious, so I for one will be staying away. I'm a pessimist when it comes to ambitious mods.