Hi. I've done about a dozen briskets now, some with my old POS offset barrel smoker and then on my totally awesome vertical UDS home made. And my friend did probably another dozen.
The flat's can work for your first time; they are a lot less work. But... you kind of miss out. So maybe next time.
If you are using a UDS smoker, keep the thing at 200-225. If you're using an offset then I think you can get away with 250, but that would just be bad. Briskets gotta go slow.
I made a totally yummy store bought flat when I wrapped it after about 3-4 hours of smoking in foil. Then let it continue until it reached 190. Let it sit for a while, etc. When I sliced into it, the juices were pouring out the top. This was made for slicing, and worked really well the rest of the week as slices for grinders.
If you'd like to have it fall apart, you gotta let it keep cooking past 200.
The temp will appear to sky rocket until like 160. Then it'll crawl really slowly. So don't use the temp change as your timing gauge.
For next time when you get the "whole packer" when you find a real butcher (not the commercialized garbage we have at places you mentioned), then with the Flat you get.. The Point. Some more yummy goodness.
You can search on line and read till your heart's content about fat up, fat down, fat off, etc. I did all that and read a lot of it. So my experience is this...
Trim ALL ALL ALL the fat from the thing.. including gutting in-between the huge fat layer that's between the Flat and Point. There is so much fat already running throughout the meat that you don't need any of that extra fat that is visible. Then rub rub rub! and you can get all the way in. The fat will not "render away", and it will just protect the meat from the smokey flavor and the rub which you're trying to get in there. So when you do this, "fat up or down" doesn't matter because there isn't much if any left. If you do this, then you finished product will have nice meat that you won't have to cut fat pieces off later.
Smoke this until something like 170-190 (longer if you'd like a harder bark) then .. (now get this!!) separate the Flat from the Point and wrap the Flat, but leave the Point on the grill, or at least that really really really fatty part of the Point. Eventually that fat will reduce some... not a lot, but it will.... well it makes me salivate thinking about it.
And again, for slicing, just cook till 180-190. For falling apart like for sloppy grinders, get it past 200. I've done 210 and still was great.
EXCEPTION TO THE FAT RULE: If you are using a vertical UDS and you are not using a baffle, the heat from the coals will be hitting the meat directly. In that case, you can leave a bit of fat and leave it on the BOTTOM so it protects the meat from the heat and will actually add to is moistness.
IF YOU USE MESQUITE, DO JUST A LITTLE BIT OF WOOD. That typically makes a brisket over powering if too much mesquite.
So there you go. I'm no expert, but I can repeat my process and know it will come out great. Science also works
meaning that reading up on "meat-science" (
http://www.amazingribs.com/tips_and_technique/meat_science.html) will help you understand the heating and melting process.
Oh yeah.. and I also got lots of advice from folks from good friends I have in TX and from OK. Still, everyone has their own opinions of what's good.
Totally depends on what you're trying to accomplish. I personally love it when the stuff just falls apart.