BMW I6 engines FTW firstly! Depends on what you want - for the E46, I would say try and find a nice 325i or 330i. Manual is always ideal unless you specifically want auto. Running costs as mentioned above is the same for the 320i to the 330i I6 engines and as such, the oil, filters and so on are the same. Bought my Wife a 320i which has facelift 2.2l 125 kw engine - has the wonderful sound but is not a 325i or 330i level of performance. Economy is I reckon as said much the same as the larger engines - I initially wanted to get a 325i for her but at the time just couldn't find a nice one, test drove the 320i and liked it! In the beginning my plan was to get her a I6, so still happy with my choice!