Ubuntu 12.04 LTS (a.k.a : Precise Pangolin) stable version has released. So if you’re using older version or the beta version of 12.04 then you can install Ubuntu 12.04 LTS or upgrade the existing one.
12.04 is a LTS (Long Term Support) release so if you wanted a stable version of Ubuntu with longer support (that’s natural -> many people are screwed due to the frequent release cycle of Ubuntu) then you should stick to 12.04 LTS unless there is any specific reason to not.
Here’s an screenshot of Ubuntu 12.04 LTS : looks pretty similar but there are lot of new cools features in Unity, specially the new HUD (Head Up Display, want to checkout – hit Alt key).
The new version of Ubuntu has a lot of changes and new features – specially in terms of performance and Unity has also improved a lot. Gnome shell interface has improved but if you want KDE or Xfce or something else, no problem. The default desktop may be unity but you can use whatever you want.
Download Ubuntu 12.04 LTS
Get Ubuntu 12.04 ISO (choose the correct ISO according to your computer architecture)