Have 2 briskets under my belt, so I don't really know, but I can sure tell what I think!
For you's who won't eat the fat, put it fat side down. Agree with most that the fat just runs down the sides as it renders. Especially if ya smoke it in a pan. That leaves the smoke to penetrate the non-fat side and ya won't be cutting away the smoky goodness that has penetrated the fat. Check out q-views of brisket. Ya see good smoke penetration around three sides, not the side that spent most time in the bottom of the pan. And the fat side in the pan will be the side sitting in the melted fat, not the good lean stuff on the opposite side. Now if ya smoke it without the pan, i'd still go fat side down, especially in vertical smokers. The same as doing butts, the fat cap will give you insulation in the event of flare-ups. Another variable is do you sear or not sear before smoking? You'll get die hard opinions to both ways. I have not yet seared, but from the brisket throwdown between desertlites and sumosmokes a couple weeks ago, you can bet your Boston Butt I'll give searing a try on my next brisket!! I feel like I'm ranting now, maybe cause of my third martini... But my spelling is pretty good!