The other thing you need to consider is the chances of delays. Given the fact that this seems to be a very crucial engagement, I would choose the one that would be the least problematic if there are delays.
I would choose either the VS direct or MAN-AMS-ATL based on that.
With the VS flight since it is direct, there are fewer chances for things to go horribly wrong.
For any connection, if something happens to your first flight, you may miss the connecting flight completely. The 2.5 connection time in AMS gives you the most cushion in the schedule. You shouldn't even consider the 65 minute connection in FRA.
You have more than 3 hours which normally would be enough for comfort. Keep in mind that getting a rental car from the international terminal involves a 15 minute shuttle bus ride, and shuttle buses are spaced about 10-15 minutes apart.
If possible, make sure you are enrolled in a rental car membership program where you can just pick up the keys and drive away, and avoid checking any bags.