I had a similar choice spread when looking for a ~10k car a month ago.
The 320d (imo) is the best choice of all of those cars, and I my many hours of research told me that the general consensus was that it was better than the IS 220d. However, for 10k you would not get one in good nick with good options like leather, and you certainly wouldn't get an M-sport. Realistically you'd have to pay 14-15k. This was the clincher for me, as for a nicely specced black is220d in mint condition with 40k miles cost me 9.5k privately. I also like the fact that they are a little more rare and feel a bit more premium. There are so many 3 series around where I live (London).
is220d makes 6th gear more of a usable gear in spirited drive (apparently). as Standard it's something to stick into at 70-80mph with the cruise on - which for me is perfect. A lot of people complain about it being unusable but for my motorway stretches it's perfect. I think you lose some fuel economy with the sport also.