I have tried all sorts of methods on my BGE and imo it is more the cut of meat than anything. If I get a good brisket, they are tender and juicy. If I get them from the local grocery store, they suck.
Fat side up, fat side down (I prefer fat side up with a place setter under it or fat side down with no place setter)
I do not trim anything from my briskets. I let the temp and time melt it all away. The 2 times I trimmed them, were the 2 driest briskets I have made so far.
If I took the fat off, I would want to cook it partially in foil or a pan to get some moisture back in.