We ate at both late in May (still sad to be back!) and had great experiences at both. Apologies in advance that I can't remember our full ordering details! I can't remember most of what DH ordered - I was too focused on my food.
Jiko was a date night for us, so our 2 DDs were not with us. We asked to look at a kids' menu, though, and I was impressed with the variety of offerings. I started with the crispy savanna rolls, which I absolutely loved. DH had the artisan cheese plate, which is pretty much always a winner for us - no exceptions here. I had the filet with the mac and cheese and was oh-so-very-happy with that choice. Our server was wonderful, and our meal was at a very leisurely pace - nice without the kiddos!
Sanaa was with all four of us, and we were very impressed. Our service was absolutely outstanding, and the food was delicious. We shared the bread sampler as an appetizer, and it was great. I had the tandoori lamb and cannot recommend it highly enough! Our girls had the sustainable fish of the day (arctic char the day we were there) and the pizza. Our older DD wolfed down her fish - it was an extremely generous portion, and she ate about 2/3 of it. Our younger DD is a pretty picky eater, and, after turning up her nose at the standard WDW kids' pizza, she devoured this one. We found out they make the kids' pizza fresh and with naan - we snuck in tastes and were impressed. I'd eat that!
Desserts at both locations were wonderful. Nothing that particularly stood out as life-changing but well presented and delicious.
The atmospheres are quite different. Jiko has the feel of a hot upscale restaurant, and Sanaa feels much more low-key. Our table was also near the door out to the savannah, so we had a decent amount of side noise. I think that can be avoided by not sitting in that alcove, but choice in that regard might be limited. All in all, I have to recommend both on food and service merits. The difference comes down to the type of atmosphere you want, I think.

Liz