Coil overs are easy to do but they have to be set up proper for your needs. The best rout is to use adjustable Koni (soft) and then based on your need adjust the spring rates. They are in my mind the best but it looks like a mix of goodies will work too. I have seen comments of switching out of coilovers but they are used on most race situations successfully and they will work great with the Impala if set up right. If your hp is not to crazy and you do it properly (and are willing to pay more for alignments) then air bags are the best for Versatility . Just make sure the bags are at the regular ride height you want the car at when the car is aligned. It is hard to keep a good alignment with bags.