If you can afford the fuel costs, go for the petrol! If you can afford the car, insurance and fuel costs, go for an E36 M3, much quicker and fantastic engines....
I have a 330d estate and as much as its a great car for woofling along on the motorway, the lag and lack of revviness make it a complete pain in the bum when you want to turn the wick up. There is also far less to go wrong with the petrol although admittedly, if anything in the engine goes wrong with either, it will sting you in a big way. Another point to factor in is that spec for spec, the Diesels do tend to be much more expensive than the petrol models which may mean it is cheaper to run a petrol over a few years than the Diesel. For reference, it is possible to get over 40MPG out of the diesel (my record is an indicated 46MPG over 200 miles but I was driving three over 60's around for the day so drove like a saint) but unless you are itching to die of boredom, 34-36 is more realistic. If you absolutely must go for a diesel, go for the later 6 speed model, the gear ratios are massively better (1st is useless on the 5 speed and the rest of the gears are really badly spaced), it puts out much more torque and power and is a nadgers more economical.
As for mapping, yes the Diesels do map up pretty well, but you have to consider that the clutches are not the strongest, are a nightmare to get out and cost a small fortune and the diff mountings are pretty well known for ripping out.......
Oh, one last point, if you think you are going to be drifting it around, think again! The E46's are big heavy beasts, will understeer worse than most FWD cars if the rear doesnt lose traction straight away, snap into oversteer in a completely unpredictable way over crests (as you find on the exit to most roundabouts) and, if you go for a Sport model with the 255 section rears like mine, have far too much rear end grip and no where near enough power to loosen the tail in the dry without applying a complete lack of mechanical sympathy. If you do go trying to drift one, make sure you learn in a space with a large run-off area and is preferably wet, you will find you need it!
