1. Pork butts are very easy IMHO. Very forgiving and easy to tell when it's ready. I've done hundreds of these over the years. Although mine have improved with time, I even found the 1st one wasn't that hard.
2. Poultry is pretty easy too. A probe therm to monitor temps helps a lot. Also training yourself not to overcook. I only cook mine to 160 in the breast. That is perfectly safe BTW. Crispy skin can be acheived at temps of 300+. Though I think crispy skin makes the finished product look pretty, I don't worry too much about it cause I don't eat the skin. Oh, and watch the smoke wook, a couple of chunks is plenty.
3. Brisket. The biggest challenge to Brisket for me is to cook long enough to be tender stopping short of falling apart. I have found if I cook it to about 185-190 and pull it, then foil and rest for an hour or so produces the result I strive for.
4. Ribs. They are kinda hard to get right. Trying to get tender before they dry out, or foiling and they fall apart. Easy to oversmoke too. I can turn out pretty good ribs (either babys or spares) fairly consistantly now, but took quite a bit of practice. Even swithching from an electric ECB to the WSM forced me to relearn the cooking part for ribs. Even though usually failures are still better than what you can get at a Q resteraunt, I've made some racks that were just plain awful.
Beef ribs are a whole different animal, so to speak, and I still can't get constistan results with them.
I've Qed a lot of other things at one time or another, and usually have pretty good results. The most important factor is three things:
1. Practice
2. Practice
3. Practice
I've also noticed the more practice in one or more areas of Q give you a better chance of succeeding in other areas you haven't explored yet. For example I had Q'ed the big four for years until I attempted goat. Though I had never Q'd goat before I'm sure much of my success was purely drawn from past successes with other meats, knowing where to turn for information, and knowing how to use that information. In other words, the more you Q, the easier it becomes to Q things you have no expeirience Qing. Just my 2 cents.