If you must have a grunty pushrod V6, I'd argue that, of your two choices ,the 4.3 is the way to go. 3.8L will make power, but the 4.3 was the "truck" engine for a reason. Lots of low end power and a flat curve.
If you aren't brand loyal, keep in mind that the 3.9 Chrysler, I believe, rated higher than the N/A 4.3L GM ever was (and it feels like it when you drive one). Plenty durable unit, just like the 4.3: it's just an old 318 small block Mopar with 2 cylinders cut off.