slamming your car will make it quite uncomfy to drive...mine is pretty harsh on sh!tty roads, shaking steering wheel...does this happen at certain speeds or all the time? probably worth getting your tracking looked at and getting your wheels checked for balancing to start off with.
coilovers is a bit of a misleading term. but basiclly on standard suspension you have a fixed platform for the spring to sit on, with coilovers this platform is adjustable so you can set the ride height however you want. thats pretty much the main difference between the two.