If you want the 14.5 then get it. Keep in mind that your climate matters too; it's starting to get hotter here, so 21 may be a bit too hefty for me.
Edited by BuffaloWang - 2/8/13 at 6:52pm
check blueowl sizing chart for all UB jeans and you can compare it there. it shows a very minimal differences in the cut, i don't own the UB 21oz yet so don't know if it stretch or shrink the same way as the 14.5 oz. that is one thing you have to consider but half an inch bigger or smaller won't harm your jeans fit anyway.