This is a LONG discussion from my perspective. I have/I've had both. From what I read from you on this thread....you should get springs/shocks....H&R Sport/Koni yellows. Coils are overkill IMO unless you get the best (AST or Ohlins). You have to worry about making sure they're adjusted right ( not that big a deal but something you wouldn't have to do with springs/shocks). And I've read so many horror stories dealing with them. If you don't have the time/patience and you don't EVER plan on going to a track (not 1/4 mile), there's no reason to buy them.
But that's just my opinion...which I think is pretty good since I've read like every suspension review on this forum along with 1,000's of other's comments/opinions on all setups. Etiher way, just search the suspension section (read the sticky) and read all you can. If/when you decide to do it....don't cheap out and don't sacrifice. Save the $$$ and get the best parts you can.
In the process of restoring an 07 335i