First off, for ANY dog the most important thing is for the diet to be nutritionally complete & balanced. If you're not using a commercial food that is formulated that way, and/or you simply prefer (or your dog prefers) to create a home made diet, the I strongly suggest you consult with a certified canine nutritionist who can create a balanced meal plan for you.
As far as which food is "best"? There is no one food that will be best for all (or even most) dogs. Especially when they reach the senior stage of life, you need to look at the specific needs of your own dog & make diet decisions based on that. There is a wide variety of health issues, both minor & major, that can start to show up in the senior years & this must be accounted for in choosing a food.
I have three senior dogs in my house (9, 11, & 13 years old) & none of them eat the exact same thing. One has early kidney issues, so we have to watch her phosphorus levels. One has some arthritis and food intolerances, so we have to take joint health and specific ingredients into consideration. One needs her weight monitored a bit, so calorie count is of primary importance. There is no one 'right' answer when it comes to food.
Edited to add - if her going off of kibble & being 'picky' is a new thing, I'd strongly suggest a vet check to see if there are underlying health or dental issues at play.