Im looking for a used BMW from 2001-2005 3 series. in general which ones have the least amount of problems. just looking for a car to drive 3-4 days a week

The 7 Series sedans tend to be the most reliable followed by the higher displacement 5 Series models. As for a 3 series, l think they all hold their own very well. l would be wary of an M3 unless it had a responsible previous owner and a good, verifiable service record.

3 series are traditionally the most reliable, followed by the 5 series. There is been some issues electrically with 7s in that timeframe.
l totally agree, about being wary of used M3s: unless it was single-owner and he/she has the maintenance booklet with the vehicle.

All the 3er is have an inline six which is very reliable for a Bimmer.

If you want a coupe go with the 330Ci, Sedan go for the 335 or 330.