As a 1 hander without shield you are relatively fast, because of the short length and low weight of the weapon. But also because weapons in the 1h class slow you down less than a weapon with the same weight in the 2h class. This is to not make shielders too slow, but as you do not have a shield you are just faster.
That is why I use a 24/15 build, I'm faster with 5 athlethics as a 1h no shield than with 6 athlethics as a 2h. The 8 ps is nice, I mostly drop people with 3-5 hits. That said, I am going for a 24/18 build on level 32.
You do not need that much WM, I get called an agi whore regularly and people wonder about my wpf. If you properly turn in your swings you are really fast with lower WM. I have 4, which gives me 139 wpf.
This is my build:
Strength: 24
Agility: 15
Hit points: 69
Ironflesh: 5
Powerstrike: 8
Athletics: 5
Weapon Master: 4
Ofcourse the difference between 21/18 and 24/18 is not at all enormous, but I really do discourage 18/21, it does not pack enough of a punch. With this build I am quite resilient, I have good damage and decent speed. I think this build is actually with 1 point to spare because I aimed it at lvl 32, so you can get 1 more IF or WM.
At lvl 32 I'll get 24/18, with 1 more athlethics. At 33 I'll max IF and have 75 hp, lol.