Most folks hold up the pastrami at the great deli's as the gold standard - Katz's or 2nd Avenue if you're on the right coast, Langer's if you're on the left. None of the commercial store-bought stuff comes close - Hebrew National, Boar's Head, etcetc... just tasteless, in comparison. They're especially bad when made "wrong", as it often is here in Boston - sliced thin on the machine, then boiled en masse, drained insufficiently and plopped on a soft, white bread bun. But even if you treat it right - buy the whole piece, steam or braise it, hand slice, serve on a decent rye bread (something else that doesn't exist in Boston, but let's not go there today) - even then, it just isn't very good.
There's a marketing distinction between the "standard" or Hungarian style, which is typically coated with paprika, and the Roumanian, which is coated more with black pepper. In truth, the main dry rub element that makes pastrami what it is, is coriander. The style differentials are infinite, and one set of spices doesn't make something better than another - although the marketing folks would like you to think so. Lean is another topic - they often market the Roumanian style as "lean" pastrami - as if that were ever meant to exist in this universe. Just about any meat can be made into any style. If you start with a leaner cut, you'll get a leaner (and dry) pastrami, regardless of the spices.
The problem with the commercial stuff is a) the preparation, and b) the cut of meat. Pastrami is done in three steps - corning (pickling, brining, whatever you want to call it), smoking, then steaming or braising. After corning and smoking, it can be (and almost always is) packaged and can be kept in the fridge or even frozen for a long time, but the final steaming or braising must be done just prior to eating. Boiling sliced meat is not an option - it is a shame. Most American deli's don't keep the whole meat on steam and slice it as you order it. The real problem with the vacuum sealed Hebrew National type of commercial pastrami is that they use the flat of the brisket. It's the leanest part, which means that it's the least tasty and the most dry. You don't have to eat all that attached fat to have a good pastrami sandwich, but you have to leave it on while cooking and trim it at the end.
You can corn just about any cut of any meat. But for pastrami, it's said that the navel is best. Some deli butchers insist that navel isn't brisket, they'll tell you it's "higher" than the brisket. Others say it's lower - from the belly. But what is it? Higher than the brisket/forearm is chuck, as far as the USDA and meat cutters are concerned. The belly area breaks down to skirts (inner and outer) and flank. Navel is not discussed under any IMPS/NAMP definition. I have found a web site that will send you a navel - but I still don't know what it is, and I can't find a local butcher to explain it to me. I will try it one day when I have some money and time, but for now, I'm trying to find something more ubiquitous and readily purchasable.
Another term used a lot for pastrami is deckle - unlike navel, deckle is discussed in the USDA IMPS definitions, although it doesn't have a specific number defining a cut. The deckle is the coarse fat and lean located between the ribs and the deep pectoral muscle, which is the entire brisket. By IMPS definition, it is supposed to be trimmed off of boneless retail cuts of brisket (IMPS 120=whole brisket, 120A = flat, 120B=point, 120C=split brisket), but in reality, most retail point cuts include much of the deckle.
And that brings me to the conclusion that for the home Pastrami enthusiast, given the unavailability of the mysterious navel, buying the point cut Brisket is going to yield the best results. The attached deckle includes a lot of fat, which keeps the meat moist and delicious through the cooking. The fat can be trimmed away after the entire process is done, but not before. There is a lot of loss - the fat accounts for a significant part, by weight, of what you buy. But the final result is much better than using the flat, which can be dry.
You can buy a point cut brisket and corn it yourself. Michael Ruhlman has a great recipe in his book, Charcuterie, written with Brian Polcyn. If you do this, remember to buy some pink salt, sodium nitrite - and follow directions carefully. Not that this stuff is particularly dangerous or difficult to work with, but a little goes a long way. And don't even think of corning without it - i.e., salt and sugar and spices alone. That can make a decent grey corned beef, but as a pastrami, it's horrible. It takes anywhere from 5-8 days in brine to corn a piece properly. Nitrite works much faster than nitrate, found in Potassium or Sodium Nitrate - Saltpeter, used since days of antiquity. (Nitrate actually has to turn into nitrite first, so it takes even longer - up to a month.) But even with the sodium nitrite in pink salt, you're still corning from the outside-in, so you have to have some patience. If you can find the room to keep it in the fridge, it will take longer, but be safer and insure a more even outcome. Otherwise, keep it in a cool area, in a crock or plastic bin.
Now here's the shortcut. Go buy a commercial point cut corned beef. But, it isn't that easy, I'm afraid. These things are so salty that if you make it into a pastrami straight from the store, it will be inedible. So you need to soak it the same as if you were corning - but in this case, you're soaking it in water to remove the salt they put in. I soak my commercial corned beef for 4 days in the fridge, changing water 3-4 times the first day, then at least twice a day.
Once you get the meat ready, whether corned from scratch or desalinized from store bought, let it dry on a rack, then dry rub. The rub needs to include ground coriander and black and white pepper. I use a spice mill to grind these plus some yellow and brown mustard seeds and a some cumin seeds, and then add granulated garlic and onion powder, paprika, and a touch of brown sugar, before thoroughly coating the meat and rubbing in with my hands. I let this sit for several hours, even a day - something I do before any smoking.
I smoke it in my smoker for about 6 hours, getting the inside to 165F. The smoker temp is kept at 225F. I use Hickory and smoke almost the entire time - at least 5 hours. In general, for low and slow cooking, I find that you need to get to about 180F for decent slicing and at least 195F for pulling. But since the pastrami is going to get steamed before final slicing and eating, it works best at 165F coming out of the smoker. After pulling from the smoker, I'll let it rest until cooled, then seal up with my Foodsaver. It will go into the fridge or freezer depending on how far out I intend to eat it. Typically, I'll make 2 at a time, eating one right away, and storing the other.
When ready to eat, I'll put it in a dutch oven and braise (water about 1/2 way up, low temp), or put it in a steamer basket (I use the pasta pot with strainer), also on a low simmer after initial boiling. I'll do this for 2-3 hours, before taking out and serving. The internal temp should be about 185F.
As good as Katz's? Perhaps not, but better than any of the commercial stuff? You bet.