First of all I've got to say that I don't drive: for several reasons which I need not go into my wife is our driver. We have a BMW Active Tourer, with which we are very pleased. Ultimately it's got to be down to whether or not you need the extra space. The Active Tourer has three seats in the back, with three sets of Isofix points, but the central seat is not wide, and wouldn't do for three adults on a long journey, so it's more of a four-and-a-half seater. You've really got to see both cars and measure up the seating and the boot.
I'm reliably informed that the Gran Tourer isn't such a nice car to drive, because, by virtue of its greater length etc., it doesn't handle quite as nicely. If you don't need the extra space, go for the Active Tourer every time.
We have the 218i, and it's economical for this class of car. At 70mph on a UK motorway with aircon on, we get 48mpg. Doing 80mph on a French motorway (the legal limit) again with the aircon going full blast in hot French weather, we get 45 mpg.
Admittedly we've got the luxury version, with quite a few extras, but we find it very comfortable. Folding mirrors are extra, front passenger seatback that drops down (so you can put in a curtain pole from B&Q) is extra, lumbar support is extra. We also like the nicer sound from the BMW loudspeaker pack, not the very expensive HK one, and that is extra. Run-flat tyres are extra, etc., etc. All a personal choice, but the cost can soon add up!