Which one is better? And which one do you like.

Surely this is just preference? They both do exactly the same thing, just one is light brown and one is dark.

I use Darnified UI with Luchaire's colors. Most of the time I use http://www.tesnexus.com/downloads/file.php?id=16387 or http://www.tesnexus.com/downloads/file.php?id=16895 themes. Sometimes I use http://www.tesnexus.com/downloads/file.php?id=16897. When I'm in the mood for it, I have even used her http://www.tesnexus.com/downloads/file.php?id=16439 theme.

They are the same thing with different coloring. Whichever looks nicer to you.

Personally, having used one then the other extensively; I prefer DarkUId DarN myself, but not by a great deal, both are excellent versions of the same UI.

Which is better? Not much difference really.
DarkUId DarN is basically DarNified UI 1.3.2 (the latest) with the addition of; to quote "DarkUI version 2.40. It also contains Darkbirdy's DarkUI Loading Screens, and the Shivering Isles DarkUI Loading Screens by HTF. It also includes a DarkUI-ified Main Menu Video and Map-Scroll Video by Fritzdog. This also fixes tiling issues with the textures in the map and inventory screens, as thanks to the amazing work of Brumbek and Belinda."

So basically a few additions and a couple of minor tweaks, but not enough to make it count as an updated version or give it a serious edge. So it is really just a matter of personal preference.

Some don't like the colour changes. For me it took a little getting used to but quickly became comfortable (My Morrowind UI is now "Dark" as well ). Others prefer to add some of the colour change mods to it as well - I haven't tried those, but they may just be to your liking.

I do use DarkUid DarN, before it was DarNified UI 1.3.2. have the impression DarkUid DarN is better somehow, just subtle..