We had a 4.4 V8 Petrol Discovery 3 HSE 7 Seat model (2005 vintage) and now have a 2012 2.2 TDCi (200PS) Titanium X Sport S-Max Powershift etc etc etc. The S-Max has a remap (Bluefin from Superchips).
We had the Discovery for about 7 months, and I really, really liked it. It was comfy, relatively quick considering it weighs more than my house, and generally a nice car.
We got the S-Max back in January, and I've since done about 8000 miles in it. It's pretty well spec'd out (on top of usual Titanium X Sport refinements I think its got a few extras like heated seats, tray tables, in door blinds in the back, pano roof and nav with reversing camera.
I like it. Its nice, its very functional, and its a good family car. The 3 middle row seats are all 'real' seats, and all 3 can have Isofix base car seats on. With an Isofix base car seat on one of the seats, you don't end up squashed in the back. 2 adults can be in there in good comfort. It's not like other smaller cars like a 3 series BMW where the rear seats are really for 2, but someone theoretically can go in the middle.
The rear row 2 seats are perfectly fine for children up to early teens, but after that, you're going to be aware of people wanting more room. All 3 seats in the middle row slide independently, so you can offer rear passengers a bit more room by sacrificing space on the middle row. With the rear seats up, we can still fit in some bags and our pushchair (iCandy Peach). With the rear set of 2 seats down, the boot is a great size. If you want to make constant use of the rear row, you should be looking at a galaxy. The roof doesn't slope down, and it makes a good difference to rear seat comfort.
I did get mine remapped, and I guess looking back on it, its offered a nice boost in performance (30bhp and 100NM tq) but does it need it? probably not. I wanted to find a good 2.0 240PS Ecoboost petrol, but simply put, this one was a good price (19k from a local Ford Main Dealer with 16,000 miles and 1 previous owner, in unsurprisingly pristine condition. It was a couple of hundred below book) and a lot of the other s-max's I'd seen were absolutely ruined inside. Put simply, I realised having a 2.0 240BHP petrol engine in a 7 seat people carrier wasn't needed. Again, why did I bother remapping? not sure.
I did drive a 1.8 TDCi S-Max yonks ago, and was actually pleasantly surprised with the performance. You don't need a big engine in these. I'd agree with previous comments that a 2.0 TDCi would be adequate.
I like the drive. Its good enough round corners, and in reality, unless its empty, your passengers will complain before your talent runs out in a car like this. It's no nimble sports car, but equally is perfectly capable on the backroads.
Hope that helps