I personally prefer a square (non-staggered) setup. The car feels more balanced, the rear wheels are slightly lighter and thus it feels lighter on the accelerator, I can rotate tyres all 4 corners and finally it's also easier on my pocket during a tyre change.
Problem is... it's hard to find used square setup for sale. Most people have staggered and to make it worse have ridiculous rear tyre widths for some reason. For example, F10s that gone to 20" aftermarket rims often have 285 or 295 rears... which I think is an overkill especially for small engines like 520i. Stock 18"/19" 245 at the rears are good enough.