If your old green IBU2 is working fine stick with it.
I am a sold old green IBU2 user. The new Ultimate wich is blue has a heavy inertia setting built is as Cirus mentioned. It is very undriveable if you intend to battle or go around obstacles. I cannot use it. Im waiting for them to release a firmware update to allow turning it off completely.
My friends use clark boards with near flawless results. The 60 and 80 offer more options and you do have to buy a remote control from a TV and a programming cable to get started unless you have a friend that is already set up but I would go with that kind of set up. If IBU doesn't get their act together I will be looking at the TK series myself when I have more tanks that need boards.