F30 has more space, has a bigger market for resale and may (depending on spec and requirement) be better equipped. The HK sound system for example is better in the 3 than in the 2, auto aircon is standard in the 320d and a ~R8000 option on the entire 2 series and some options like Heads Up Display is not available at all on the 2 series.
The F22 is lighter/more agile than the F30 and certainly less common / more rare than the 3 series. It's also (depending on specs) around R40k cheaper than the 320d. You can get into the 230i for about the same price as the 320d. Please don't take it the wrong way, but coupes are usually associated with being sporty and (as GREAT an engine as the B47 is) a petrol engine may be the better way to go for a coupe.
Try and drive or, at the very least, sit in both (as close as in the spec/ price level that you would be interested in) and make up your mind from there.