Not trying to drag out H's thread...found this on 'the other board', and can't vouch for the stats, as they aren't linked, but fwiw:

cargo capacity w/rear seats up:
X1: 14.8 cu.ft.
E91: 16.2 cu.ft.
A4: 17.3 cu.ft. (B8 Avant)
F31: 17.5 cu.ft.
X3: 27.6 cu.ft. (F25)

cargo capacity w/rear seats folded:
X1: 47.7 cu.ft.
E91: 48.9 cu.ft.
A4: 50.5 cu.ft. (B8 Avant)
F31: 53.0 cu.ft.
X3: 63.3 cu.ft. (F25)

Not apples to apples, as I am not pumping Hyundai Tucks, but my CEO's H Tuscon has ~26 cubic feet of space in rear cargo
compartment with rear seats up, almost equal to the X3, if rear cargo is important to anyone. Quite a diff vs the X1...
GL, mD

I chuckled when I saw the pic with the all-mountain bike being fited into the cargo area of the X1. A real Downhill mountain bike is not going to easily fit in the X1, I can tell you that. On my X3 I can stack two on top of each other with the front wheels off but then there's not much room for the remaining gear (floor pump, helmets, body armour, backpacks, etc....). Even then it is a tight squeeze and requires finesse for the handlebars and front fork, and I have marks along the backsides of the front seats from tires rubbing.

Abysmal interior space, low interior quality, good looks, good performance , reasonable price , but we decided to go F30

Good choice. Actually I like the F31 touring. If they made a lower-model 320d version I'd go for it. When I drove the X1, I thought it drove well but that was about it. I also drove a Tiguan Highline ("Track and Field") and that was a better overall car even if it wasn't as crisp in driving dynamics.