I'd say Mara...
Not necessarily because the food is soooo spectacular - though it is very good - lots of standard c/s choices, along with African Stew, delicious soups and desserts - but the resort is really great to walk around.
You can grab your lunch, eat outside near the pool, then head over to the flamingo pond and look out over the savannah to see some of the animals. Then walk out to Arusha Rock for a different view and chat with one of the guides there. And if the weather doesn't cooperate, there's lots of native African art inside that really is beautiful, and there's lots of indoor areas that overlook the savannah's for animal viewing too.