If you wanted to go as a handler/dog team you would need to go to the basics/transition workshop. If going as an observer you could go to either.
I wouldn't say you will learn more at the advanced, but you will likely see different issues arise in the basics/transition than in the advanced. You will see troubleshooting work on the actual issues that arise.
In the basics/transition that I attended we saw troubleshooting on things like line manners, bird handling (sloppy holds & dropping birds and munching), shopping the pile, sit to pile, swim-by, water tune-up drills. These sessions were mostly if not all done in the yard rather than field. The yongest dog was 9 months and was just starting TT. The dog that was farthest along had started swim-by.
In the advanced that I attended we saw troubleshooting on things like line manners (Lardy commented on how bad line manners are on clinic dogs - low standards), crooked sits, auto-casts, out of control on blinds, recalling (picking up the dog). There was more of working on problems in the field than I remembered from the basics/transition. For example, some dogs had issues with head swinging, so the handlers would run a given field set up so that she could work on the issue of head swinging. Some dogs had problems with secondary selection, so they would run a set up to work on that. Youngest dogs were preparing for Qs, most advanced dogs were running and placing in AA stakes.
If you still have a ways to go in transition, or if you are near the end but feel like you may have some things that you need to clean up, I'd go to the B/T.
I will add this about the advanced workshop, and this may vary depending on who attends (especially as a handler)...
Experienced trainer/handlers will ask some very good questions that spark discussion about how to approach a test or deal with an issue. Listening to Mike and Laura Parrot (1997 NFC Lucyanna's Fast Willie), discuss how to run a set up in training versus during a trial or how to work on head swinging with this particular set up was very informative. These types of conversations probably only happen at the advanced workshop.
BTW. At least two of the handlers from this springs advanced clinic that were preparing for the Q had wins this year, Laura Parrot took a less than three year old Pirate pup, to the 9th (I believe) series of the National AM, and Lois Atkins won the Canadian Open with the dog she brought.