When I pull the trigger on a kamado style cooker it will be the Weber Summit and here's why.
~No ceramic to crack.
~Lighter to move around.
~If you dump the Weber over, yes your gonna be pi$$ed cause you dented it, but it will still cook as opposed to being in pieces.
~Comes with everything you need to get the most use out of it as opposed to buying separate parts.
~Stainless gasket mounted on the lid where it should be.
~Can do reverse sear without having to remove any hot parts from the grill.
~Better hinge system.
~No checking lid alignment with a dollar bill.
~Lid is lighter and much easier to raise and lower.
~Price is the same once you load out the BGE XL the same as the Weber.
Note, these are observations I made by going and looking at a BGE XL and the Weber Summit and doing a comparison. I have no experience cooking on either one.
I'm sure there are other reasons but this is just off the top of my head. As far as actual cooking goes, I'm certain they would both perform equally well with the exception of cooling back down if you overshoot the desired temp. I've read several places that to bring a ceramic cooker back down in a reasonable amount of time it's best to put a pan of water in it to serve as a heat sink where the Weber will come back down quicker.
Babyback was thinking about doing a side by side cook off between the Weber Summit (top of the line steel Kamado) and the Komodo Kamado (top of the line ceramic Kamado) and seeing which one wins. That would be cool!
