I disagree about the tri-tip - works great in these smokers. Use the low-temp method I use for prime rib, smoke to about 128-130 (depending on medium-rare to medium), and reverse-sear on the grill. Tender and juicy!
As for grades of beef: Select briskets are fine, if prepped right. I brine briskets, and inject, so even a cheap select cut is good. I've smoked Choice and Prime briskies, and can't tell much difference. You see the difference much more in something that is not cooked to such a high internal temp, like rib or sirloin tip roasts. If smoked right, you won't tell much difference between Choice and Prime - except in the weight of your wallet!