Coilovers when coupled with good quality struts are generaly a better idea than springs if for no other reason than that they are adjustable ride height. Coilovers generally come with a higher spring rate than just springs do so they are generally more performance oriented.

Strut bars mount from strut housing to strut housing and help torsional rigidity and keeps the struts acting as one solid unit. Sway bars mount on the underside of the suspension and do just what the name implies...it keeps the car from swaying when you take a corner by displacing stress and pressure evenly across the front or rear suspension (whichever they are mounted on). A higher tensile strength sway bar will make the car handle more level in the same corner as one mounted with a stock sway bar (usually a softer rate for ride comfort moreso than handling).

Hope this helps some.