Although they're all fundamentally the same cars, as T_B said, each manufacturer has added their own mark on their models so to speak. As far as I know they all have matching suspention componants too, however, that doeasn't necessarily mean that they all use Ford's, lol. Infact as the Ford uses the VW group diesel engine, as does the SEAT, all three might actually be more VW than they are Ford. I personally would go for the Sharan as I love the blue backlit dash lights...
That is really all that sets the models apart to be honest. It all comes down to badge predjudice really, and another snall tip...The VW will always hold its value better, which is good for selling one, but not so good for buying one. Bear in mind that any of the vehicles you chose would have taken the most depreciation that they'll ever really have, on leaving the showroom.
