Hey Mike, I am a new guy here also, but have learned a lot as a visitor for some time.. from Jersey also.
I went through the same thing you are deciding on and went with the 22.5. You can cook efficiently with 22.5, there are a couple of easy ways to do it, and you can cook larger cuts including full briskets and full length sections of ribs.
That was important to me, because those are trickier to cook in the 18.5. Though I believe from what I hear that it is more efficient with fuel.
So welcome and you will enjoy either.