We have a maxicosi Tobi (cos the priori XP wouldn't fit in our Nissan Qash n Qarry) and fits brilliantly Morgan Kate loves goin out in the MINI.
she likes especially likes watch the clouds out of her sunroof!
We also use a quinny zapp which fits in the boot or even on the floor in front of her...also we used to use a Bebe Confort Loola travel system and again that fit great but leaves no boot space...