Wow that’s a tough one. GOR and Kangaroo Island are both stunning and very unique. Maybe have a look at the posts on our site on GOR and KI and see which one may grab at your more. I’m finding it hard to recommend one over the other!!
I can’t remember the drive much from Alice to Uluru. We had just spent 10 months in that landscape so I could have been a bit blase about it then and not paying attention. I don’t think it changes much. That area is pretty much flat red desert. Maybe flying might be better if you are short on time. There are beautiful areas around Alice Springs and there is the awesome Kangaroo Sanctuary but they aren’t on the way to Uluru You could go the long way via the stunning Kings CAnyon and East MacDonnell Ranges but that would add a lot more time to your journey I think