Getting 21 strength and not getting a strength-based skill to 7 is a really bad idea.
21/18
7 power strike
6 athletics
4 shield
6 weapon master
18/18
6 power strike
6 athletics
6 weapon master
6 ironflesh
5 shield
18/21
6 power strike
7 athletics
6 weapon master
4 shield
For the 18/21 or 21/18 build, you can drop 3 weapon master for 3 ironflesh if you feel squishy. I think I'd recommend 18/21 the highest if you're going high level. 18/18 is a nice build if you'll retire at level 31.