My first Guild was a Westerly JF30 12-string. I knew nothing about the brand before that one, which turned up on my local Craigslist.
The seller started it at a 1000 bucks and dropped it by 100 dollars each week. When it got down to 600, I decided to go check it out. I was flabbergasted. I had two Taylor 12s at the time, one of them their Leo Kottke Signature Model. The Guild sounded better to my ears than either of those, though the Taylor neck profile was more comfortable than the Guild.
I sold one Taylor, kept the LKSM, and began checking out every Guild 12-string I could lay my hands on. I've had more than a dozen over the years and still have seven now, my favorites (all jumbos), including a Westerly F412.
I agree with Taylor Martin Guild -- my JF30 12 and F412 are pretty close sound-wise. There's possibly a bit more volume to the F412, but mine have good bass response (more than my F512, which I sold); both are clear between courses of the strings; and unlike some 12-strings, neither is mushy in the mid-range.
I have since played two other JF30 12s, neither of which sounded as good to me as mine does. So they aren't all created equal!
But I suspect if you were blindfolded and I played the JF30 and F412 back to back, you'd be hard-pressed to tell them apart.
If the price is right, I recommend checking out any JF30s that come your way.