When you're buying meat for the barbecue, remember that if you start with good raw material then you're more likely to get a great finished product. Here are some tips for choosing wisely at the butcher counter:
More fat means more flavor. A well-marbled piece of meat is going to fare better on your grill or smoker than a leaner cut. And, especially for slow cooking, the "luxury cuts" like filet are exactly wrong. You want the cuts that come from the working areas of the animal and have more fat stores.
Fresher is better. Poke the meat you're considering (if it's wrapped, that is). You want it to feel firm and to bounce back after you move your finger away. If it doesn't, it's probably been on the shelf for too long.
Liquid is a bad sign. The red juices you see pooling in a package of meat mean that the meat got too warm. It won't taste as good or be as tender as meat that has been properly refrigerated.