If I had to choose, for me, which flight to take, I would go for Group A, but for some different reason than the ones you highlight:
- I have no problems in doing a number of layovers
- I like to fly to/from different airports
- I don't want to waste my time waiting for others.

However, if I still were a 17yo boy, I wouldn't give a s**t of these details and prefer to go along with my friends.

This is the same topic as the Pisa trip: of course Firenze is much more interesting than Pisa (which is good, as you state, for a selfie at the Leaning Tower and nothing more), but the problem is that I bet your grandkid has different interests from you.
I'd remain in Firenze, or better I'd propose a trip to Siena or Arezzo.
But I'm 38, not 17! ;-)