Hi.

I haven't played WoW for about a year after and having come back to it have had to do  a full re-install.

I used to use TitanPanel and was quiet pleased with it but there must be newer UIs about.  Spartan UI looks good just for how much screen area you preserve.

Which UI do you guys think is best?

If you are more the minimalistic guy, i´d prefer Tukui (http://www.wowinterface.com/downloads/info12688.html) it looks awesome, is lightweight and totally small.

Titan isn't a UI.  Also, are you looking for a UI suite or a UI compilation?  The difference is that a suite is a standalone addon, and a compilation is someone's WTF folder in addition to their addons folder, and you delete your WTF and Addons folder prior to installation.  UI comps are made up of lots of different addons, while a suite is something more streamlined.  SpartanUI is a suite.  Be sure to visit the forums for SpartanUI if you're thinking of downloading it, as there is lots of information available there.