if you get coils you can adjust the height........raise it up begining of winter....slam it in the summer.......and you can maintain what your stock height was on most coils if i am not mistaken.....
if you never plan on changing your height you may as well do new springs and something like bilstein dampers.....it would be cheaper if u dont plan on utilizing the coils adjustability
2005 Evolution 8 - Current
2007 SGM/coral e92 335i - Sold
2009 BSM lci e90 335i xdrive - Sold