24/15
5 IF
8 PS
5 Shield
5 Ath
0 WM
Better than 21/15. You lose only one hit point and get one more PS. You don't need WM as a shielder. 21/18 is also very good.
I'm minusing this post not to be a dick but because I believe it's false information. You aren't taking into account the damage bonus that the 5 WM of the 21/15 build provides.
Ultimately, the 24/15 build provides
very slightly more damage than 21/15, at the cost of a
slightly slower swing speed and a
very slightly smaller hp pool. I personally prefer 21/15 as a level 30 build, however if you think you're going to go above level 30 24/15 might be better because it has more room for you to grow into.
Really though they are both good builds and there is very little different between them.