So I managed to get me a PC copy of Oblivion and now have the power to finally do things that was never possible on the box.

Rebuilding Kvatch is one of these.

I had a good look on nexus and I can't really decide which one is worth downloading.

Some sound off from their descriptions.

So what would you recommend for a mod?

The problem is that right now, the one Kvatch Rebuilt mod for which there is the most third party support, named just "Kvatch Rebuilt", is hidden at Nexus and has been for a while, theorically until its version 3.0 is released.

In the meantime you can download http://tesalliance.org/forums/index.php?/files/file/1180-kvatch-rebuilt/