Just purchased a used e90. The previous owner installed a set of eibach spring coils but the damper was not in good shape, with the rear ones leaking oil.

Should I change dampers to something like b8 or should I change coils and dampers to OEM (or near OEM) spec? This would be my daily driver. Are those dampers for lower ride heights terrible at daily driving?

Undecided

I have stock sport springs, but on previous cars had H&R lowering springs with Bilstein Sports... ride was great, loved them! If you have lowering springs in there, you should have the correct shocks to go with them. Bilstein B8s would be the way to go. Get new mounts at the same time. How are the fronts, and what are they? I can't imagine someone would go to the effort to replace front springs and not the struts, but I guess it happens. Rears should be easy to swap out, and you can do front struts at a later date when they're needed.