Shield Block Rate VS Block Strength

So which is better?

I'm a lvl 50 PLD and my lowest piece of equipment is
"Scorpion Shield" block strength 36 block rate 200.

My own guess is higher block rate would make damage more stable and less violate and higher block strength would reduce the damage when blocked.

If you're a 50 PLD, why don't you have a kite-type shield? There's no reason not to use one when available.