What is best griddle plate for 22” Weber Kettle?

Do you have a Slow n Sear? Their Drip and Griddle pan goes right over the top of the SnS to make a griddle and also works as a drip pan when you aren't using it as a griddle.

It's pretty versatile and heavy duty.
Drip and Griddle

If you're not familiar, here is a picture. The Slow n Sear is at the top, and the Drip and Griddle fills out the rest of the space, keeping all the grease from dripping into the ashes, below. That make cleang the grill a snap, as only dry ashes make it all the way to the bottom of your grill. When you want a griddle, just put it on the top grill above your SnS.