kurt --
Extremely difficult question -- and nugget hunting is not something where you can just pick up a detector and head out, and expect to find gold. Learning your machine (which takes time), and THEN learning about hot rocks, cold rocks, mineralization, proper ground balance in ground of varying composition...there's alot to learn.
THEN, it matters what KIND of gold you are looking to find...very, very small flakes? Slightly larger flakes or small nuggets? Larger pieces? Gold in quartz or placer gold?
The Gold Bug Pro is a very good gold unit...that's what it was designed for. The Pro and 5" coil (or the new 5x10" coil) would be good choices for small gold; for VERY fine gold/VERY small pieces, the old Gold Bug 2 is the better unit...but not the easiest unit to use until you learn it; much less user-friendly than the Gold Bug Pro. Gold in quartz, especially just very fine veins, can be very tough to detect, as the non-uniform shape of the embedded gold generates only weak "return signal" to the unit...
Anyway, I am just trying to be honest with you -- if you want to find gold, there is quite a bit to learn, first (been there, done that...I learned very quickly that finding gold is a learned skill, not something a newbie, like myself, is going to "hit the ground running" with...)
Steve