You know, higher = better
LG is the only I know which can burn 24x to MCC, Liteon and Samsung can only do it for TY. But to have agood burn with these speeds are not easy.
Do you have no Pioneer DVR? Pioneer overspeeds a lot media, 24x is only possible with TY. But 20x is possible with UME02, AML 003, MXL RG04 (rare media), 18x with CMC MAG AM3, OPTODISCR016.
But even I don´t dare to use these speeds on specific media, except I only burn >3,5GB