Well......
I have both machines and have used both quite a bit....
Both machines are GREAT and you can't go wrong with either one.
Generally speaking I would recommend the AT PRO for coin hunting and trashy areas like parks, beaches.
I would recommend the AT Gold for more for the prospecting, relic hunting, non trashy areas.
Given all the same conditions, coils, etc. The AT Gold will beat the AT Pro on depth when using its 'ALL Metal Mode' but only by an inch or two at the most (when using the two stock coils)
Each has its own features that make it more suitable for certain situations.
I like the AT Pros adjustable notch discrimination on ALL its modes. The AT Golds is fixed and cannot be adjusted at all.
The AT Gold has true All Metal mode, adjustable ground balance window, and a few other nice features.
The AT Pro works (not the greatest, but does work) in salt water, the AT Gold pretty much does not.
The AT Pro is a little quieter overall, the AT Gold is very chatty.....that's partially because of only have 3 modes and the fixed discrimination.
So, after using both machines I really feel that it comes down to what type of hunting are you going to be doing...and what features do you really want/need.
Some of those 'advanced' features are only useful in certain situations.
Everything said....I use my AT Pro a bit more than my AT Gold. I have all the Garret coils (concentric and DD) except the 4.5 Sniper. Prefer the DD coils. (highly mineralized soil and target separation).