I am in my first active duty year and did not do an AEGD (I am in my snowbird year waiting to begin specialty training next summer). There is another dentist in my clinic that arrived the same time I did. He just finished an AEGD. My practice is COMPLETELY limited to exams and operative. He is doing impacted third molar extractions and given an assistant who fills his preps so he can see more patients than I can. Granted, I am at a post that probably limits GPs more than any other in the Army but the point is that the AEGD is valued by commanders and probably will give you expanded privileges no matter where you end up. Additionally, when coming straight out of dental school there is a learning curve in the military (e.g. different record keeping, computer software, materials, philosophy of practice) that will take time getting used to. Learning this within the environment of an AEGD would be easier than getting thrown into it like I was, which was pretty stressful. In my mind, if you think you will remain a GP or need time to figure out if you want to specialize, an AEGD is the best path. Even if you are picked up for a specialty right out of school, the AEGD will be worth it. The fact that it is not a payback year shouldn't play into it heavily. After all, the four years of dental school weren't payback years either yet they were well worth it.
There is no doubt that the AEGD will expand your scope in the military (especially in the early years) and is the best choice professionally (I chose not to complete an AEGD for personal reasons but it definitely set me back professionally).