Personally I don't consider these two on the same level - Jiko is hands-down one of the best restaurants in Disney and has been since opening...it's a Signature dining restaurant and definitely earns it with excellent wines and generally better service...plus a creative menu full of interesting and exotic flavors and spices.
All of that isn't to say Sanaa isn't great - I very much enjoy Sanaa and often go there - it's just not Signature level. The menu doesn't change much - it's not 'all you can eat' or 'family style' but the way you select from groups of food categories to make a dish has a more casual family style feel. And service is as good as most Disney table-service spots - which I always have good experiences with Disney staff - it's not quite up to the level of attention at Jiko. I haven't had a bad meal at Sanaa and it continues to be a restaurant I'll book regularly when I go to Disney World.
Jiko is probably slightly less kid-centric - a lot of adults tend to dine there and there aren't animals roaming outside the windows and such. I still see kids there and some seem to enjoy it, but it's a quieter, a bit more spread out between tables and booths and seems to cater to long, slow meals with appetizers, wines, meals, dessert and coffee after...I often end up spending well over an hour there enjoying all the courses. They have the typically-Disney dress code requests, which just means try to avoid sloppy t-shirts and bathing suit shorts. The waitstaff is usually from African nations (there are some that are not), and they'll happily discuss their home country and the food and spice inspirations - they're also very well trained on helping with recommendations both for food and wines. You get hot rosewater scented towels to clean your hands before starting the meal...the overall feel is more upscale.
And I have to put in a comment on bread service - while Jiko only provides two breads and a flavored butter - personally I find the giraffe bread to be the best, most delicious bread in WDW. I love Sanaas various spread options and enjoy their bread service too - but Jiko holds its own with just two breads and baobab-citrus butter.