Some have rated the S-max as a better tow car as it is a more "sports" orientated vehicle and has stiffer, more heavily damped suspension.
Supposedly, below the window line, the Galaxy/S-max are identical but I'm not sure whether the 3rd row of seats in the Galaxy have you sat on the floor as they do in the S-max, I'm 6'1" and can easily sit upright in the 3rd row of the S-max, there is actually more headroom than in the old Galaxy but you're sat on the floor with your knees up to acheive this.
Most people prefer the looks of the S-max, rather like a hatchback on steroids than an MPV.
We chose the S-max over the Galaxy because
It was much cheaper
Better looking
Better to drive
The additional space in the Galaxy isn't actually that usable for us.
It tows our 1600kg t/a caravan through strong crosswinds with barely a flinch but front wheel drive and a tall reverse gear are a pain at times. A 4wd S-max would be a fantastic towcar. I don't go offroad and have no use whatsoever for a car with any offroad capabilities thats big on the outside and no space on the inside but I would like a decent 4wd MPV.