Been discussed a million times on here. Look for a thread which was prominent about 3-4 months ago which discussed many different setups.
If you want Rolls Royce then get Ohlins (fully adjustable)
Great high mid range and tuned specifically for E9x then get the Birds setup.
There are plenty other Bilstein setups et al which are detailed in the thread I mentioned.
Go search all the info is out there.
Personally I have the Birds setup and it's the best money I have spent on my FBO 335i.
Ps: just doing springs is pointless unless you just want a visual job and don't care about ride quality
Engine Mods: JB4 G5 ISO, BMS Backend Flash, BMS DCI, ETS FMIC, ER CP, AR Catless DP's, BMS OCC, BMS Cowel filters & Forge DV's.
Running Gear Mods: VMR 710's, Birds B3 Suspension, Stoptech Grooved Rotors & Yellow Stuff pads.