One should only choose a third class if for some reason you don't like your current combo mix, or you don't care and want to try something new. It just complicates your leveling and gear allocation. IMHO, if you really wanted to try out R/Wd or say R/W, make a new toon, but stick with your current R/S or S/R, either one is good, the option for a third class was given so Runewaker could make more money.