You must do a lot of considering about the hunt areas and type of gold you expect to find. Any of the mentioned detectors will find a large and some small pieces of gold on or near the surface. If you are going to hunt in trashy areas like creek bottoms where the ground is uneven and there are lots of "hot rocks", auto-ground balance is helpful. However, discriminating out some of the trash might cause you to miss the nugget. If the targets are buried in highly mineralized soil, you probably will strike out. Operator skill and experience can make a big difference, but only super sensitive detectors like the 17-18000 and SD series will do the job. If you want a multi-purpose detector, pick the one whose features you prefer. Regards and Good Luck!