The choice is up to you. Baby back ribs are naturally tender, and have ample meat between the bones. Spareribs are probably the more economical choice. They are also generally quite a bit less in price. My personal favorites are the baby backs.
Smoked chickens are delicious.
Look for nice plump birds. They should be fatty enough to stay moist during the long smoking process. If available, capons are a good choice. I've also found that free-range chickens tend to be fattier, and the fat is firmer, and stands up to long cooking better. Believe it or not, I've never smoked a turkey.