Bushtec, Rivco, and Add On all mount to frame. Others (Kury, et al) mount to sub frame, avoid them.
Bushtec & Add On are a vertical receiver behind & under the fender. Rivco is a horizontal receiver through the fender. Player's choice, either approach is fine. 2012+ GL has a fender that sticks out a bit further and requires a longer ball mount than 2010 and <, i.e. further back from wheel just to clear the plastic. Physics works against it. Not too big a deal. Length of ball mount is only different between model years in Bushtec <=2010 vs. 2012+.
The Bushtec vertical receiver is semi standard and you can find aftermarket options if you need them, e.g. Curt. I think the Rivco is more custom so harder to find. Though not as if you'll be buying a ton of ball mounts.
Bushtec seems to be the standard. Rivco is fine. Add On seems to be the dark horse, less expensive, still frame mounted. Pick your poison. No reason to get inferior mounting approach of Kury, ShowChrome, etc.
Pin vs. ball mount needs to match your trailer. If you don't know, get ball. Only reason for pin is if you have a Bushtec pin mount trainer. You can exchange pin for ball later.
Bushtec deluxe adds mud flap. Not a bad idea. You can hack one if you're handy and cheap.
+1 to isolator. If you have a Tailwind trailer, it already has one on board so bike side is nice but redundant. Otherwise, it is very nice and prevents trailer wiring problem from frying bike harness. There's no connection between isolator and harness, so buy whatever. Bushtec is decent. Electrical Connection is another well regarded one. Get one with a pin out that matches your trailer. If unknown, 4 pin is common but 5 or 6 pin (with adapter to 4 as needed) is most flexible.
Tow wisely. Welcome to the neighborhood.
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