There isn't really much differences between the engines, it's just different injectors, and on the on the 140ps they have a variable vane turbo.
The earlier transits suffered from piston failure due to over fueling, but this has been sorted with a PCM update.
There aren't any major problems with the transits, but like and diesel, they will suffer from injector problems and EGR problems eventually.
also all mk7 transits have DMF, and again with those they will fail, but they and last 30k or 150K.
Whenever you read of someone that has had problems after very low miles are always the minority. I've got a mk7 transit on 90K and it's been fine.
I personally would go for a 115/125ps, the extra power would make the drivability of the van nice and they are also 6 speed.