A common complant of some coil-over kits is the odd noises them make. The twang is usually when the spring unseats due to the suspension extending, and then when the weight returns the spring sometimes hangs up on a collar and then twangs into place once full weight is on the spring.
90/10's are a drag shock in general. They are designed to easily extend and then slowing compress.
With a drag type suspension, you will experience some draw backs on the street. So if you want a better ride, a better quality street strut may offer a better ride.
Some coil overs do ride quite well. I have max motorsports coil overs on Bilstien struts and my car rides VERY good up front and doesn't make any noises. Coil-overs, with a good strut, do provide some ride benefits due to reducing the friction of a standard spring and putting the spring directly on the strut. But to accomplish this, the spring length, rate and strut all need to be matched up.