Well I would personally go with the TRD-Off road package.
I currently own the a 2004 Tacoma with the TRD Off road package and love the ride in the dirt.
As for the Differential lock pretty sure u have to stay in first gear, as I have hardly used it,
but is has gotten me unstuck without any effort. (IMG:
style_emoticons/default/clap.gif)
TRD Sport Has:
Sport Tuned Bilstein Shocks
TRD Offroad has:
Off Road Tuned Bilstein Shocks ( heavier Dampening Rate)
Progressive Rate front Coil Springs
Off Road Cambered Rearspings to compensate for wheel travel in offroad situations
Larger stabilizer Bar
So the bottom line is the TRD Sport Has a smoother onroad ride while the TRD Off Road is rougher on road, but more equiped for rough terrain.