We like a 12-14 # (6kg) brisket. You want a good layer of fat on top. Don't score it. You don't want one that has too much fat marbled into the point cut. The best to pick one is to try to wiggle the brisket in the middle of the point cut ( thick end), Oh did I mention that you want a whole brisket? At ant rate, the ones that wiggle most easily will have the leaner points. If you get one w/ too much fat marbled into the point, the point will be too fatty to serve sliced.
We also believe in searing the brisket (totally black) before smoking in order to achieve caramelization. I posted a poll and started a thread on this subject. As I recall it was most controversial, and most who responded said they'd never tried it. We have, and as a result, we never do it any other way.
Now, I'm not sayin' that you hafta try it that way, but for our $.02 worth, it's one of the most important steps toward the perfect brisket.