Well, if you've never driven offroad before the T4 would be much better than the B4. It is much more forgiving to drive. I have both and most of the time pull better lap times with the truck than the buggy.
Both are durable, easily tunable, and very easy to build. (As long as you follow the instructions carefully)
Which ever you get make sure you upgrade the bumper to the blue aluminum one and change upgrade your turnbuckles to the blue aluminum's or Lunsford's.
I would lean to the T4...
Also, go to www.rc10b4.com
This is a website dedicated to these vehicles.