I got the 8-qt Duo. I wasn't really interested in the Duo+ or Ultra with the additional yogurt or pasteurize/sterilize settings, and IMO paying for the egg setting is a waste since eggs are one of the easier foods to cook with the manual settings. I did want the extra capacity for larger pot roasts, and because I eat dinner leftovers for work lunches.
It was well worth the money because my cooktop died right after Thanksgiving last year, the cheapest replacement I could find was $600 so I haven't bothered with getting a new one yet, and since I can fry/saute foods in the Instant Pot I actually don't miss the cooktop.