Seriously. This is one of the most flavorful roasts. It's essentially foolproof, and is so, so easy. I think the difference in tenderness is the cut of meat, but I don't know one specifically because I just buy whatever is the right size at the right price. Cheap-o over here. But regardless of the cut, the meat will come out juicy and so very yummy. The carrots and potatoes are totally optional, but they absorb the flavor really well, and make this a more filling, more complete dish. And I totally eyeball the amount of veggies, so do whatever you think will work for the size group you are feeding. The type of potatoes you use is very flexible, just don't use russet (baking) potatoes. Red, yellow, white, or fingerling are great. And if you use fingerling, just cut them in half, maybe thirds, not eighths.
Low and slow is the way to cook this- I've forgotten and had to do it on high, and the meat just isn't as tender. So low and slow. If you need to cook a roast larger than 3 lbs, I'd add another jar of peppers and use maybe half the juice for each pound over 3. Just to make sure there's enough juice in that baby. If your roast is smaller than 2 or 3 pounds, use the whole jar anyways. Can't hurt. :)
Crockpot Peperoncini Roast
2-3 lb beef roast
1 jar peperoncini peppers
1 lb mini carrots
3 or 4 red, yellow, or white potatoes, cut into eighths
Place the potatoes in the bottom of the crockpot, followed by the carrots, then the meat. Dump the jar of peperoncini, including the juice, over everything. Cook on LOW for 6-8 hours.
So. Much. Flavor. You'll want to feed it to all your friends. Just don't tell them how easy it is!