Generally top floor condo units have vaulted ceilings, which give you a feeling of more room and of course no one above you!! Having a lake view (even if limited) has value. Also, if you're considering using the condo for nightly rental, upper units will usually earn more per night. The advantage of the bottom unit will be savings on utilities. They will usually stay cooler in the summer. Also, if you have children or a dog, being able to walk out the back to the lawn and lake is a big positive. And with children, you don't have to worry about disturbing anyone below with their 'active feet'.
Hope that's helpful. I sell lots of condos in the Branson Lakes area and it really becomes a decision that you need to make based, not just on price, but how you'll use the unit. What's right for you and your family?
Definitely use a Realtor to help with the negotiations. He or she can also provide recent sales data to help you make an informed offer.