Ventajas
Great camraderie and culture (some office locations are friendlier than others!), interesting and varied work (doing project vs program work will largely influence this - ask about which one you'll be doing if you're applying for a general AA posting), excellent benefits (good healthcare coverage/prices, commuter benefits, great PTO accrual and sick time, etc.), pretty good pay. I also have fantastic work-life balance (I rarely think of my job after 5 pm) and the flexible work schedule is nice. I'll stick around here as long as I can!
Desventajas
Your experience will largely depend on which researchers you work with. Some researchers I've worked with have been the most fantastic leaders I've ever met, and have made my job here a genuine pleasure. Others have been less great. Expect to do lots of "managing up." Again, some will appreciate this, others will hate it, even though it's part of your job. This is minor, but AAs are some of the only hybrid staff who are required to be in the office a minimum number of days each week (currently 2 days). The people I support are rarely in the office or are located elsewhere, so commuting just to sit in virtual meetings feels kind of silly, BUT the offices are newer and comfortable and well-located. Our paid holidays are on the lower end of what's common in DC with your federal employee peers, which is kind of a bummer.