The build that works best for my playstyle is strength 21 and agility 18. I dont use armor with this char. But the shield makes her very very slow so that a 2h/polearm tincan is as fast as my shieldmaiden.
When you want to use armor, well, good luck against crushthroughers, unarmored 2h/polearms and with catching archers.
Do you play NA? EU, the best (or at least most of them) shielders dont use armor. No armor means you can compensate the less athletics and the shield extra weight you have to deal and live with. But the power strike 7 is necessary. Keep in mind, your shield cant take many hits. With only 3 power strike you would have to hit a tincan 5,6,7 or more times perfectly to kill him while he needs 1 lucky hit on you to insta kill you.