Have you driven the Merc?
I drove the A250 twice while searching for a replacement for my 1 series. It was between the A250 and GTI. Now i LOVE how the A class looks (particularly the facelift) but found it sooo disappointing to drive.
I found the cabin to be very dark and a little claustrophobic - the pillars are very thick making the windows small. The engine has a nice sound to it but it's completely blocked out by the high levels of wind and road noise it really was noticeably particularly at 75 on the motorway - getting back into my 1 was just so much more refined.
I really wanted to like it because I love the looks - ended up ordering a GTI instead and can't wait for it to arrive!