I use a 6 quart kitchenaid bowl for mixing and baking? For my genoise cake batter folding, which size balloon whisk would you recommend- 14 or 16 inches? I can buy only one. Any brand recommendations?

the only one i would recommend is the one from JB Prince, and it is 14.5” diameter and 18” lenght.  the brand is matfer and it is from france.
i don’t recommend a traditional balloon whisk of those dimensions.  it will be very very heavy and the wires pretty thick.  it will be hard and heavy on your hands and on the batter.  the JB prince one is lightweight and really the ultimate tool for folding on the KA 5 or 6

part number U605.  JB Prince - 212-683-3553 or 800-473-0557