Type of wood
Gas grills serve their purposes, and some respectable barbecue joints will run smokers with gas assist functions due to spatial or time constraints, but there's no substitute for the flavor of burning wood. But wood isn’t monolithic. Milder woods like oak give a cleaner, lighter smokey flavor, fruitwoods impart a subtle note of sweet flavor, and mesquite adds a richer, fuller smoke taste.
Charcoal, wood chips, or pellets all have their relative advantages: charcoal burns longest but has the least woody flavor, chips will add a punch of extra smokey flavor, and pellets typically offer the pitmaster the highest degree of control over whether they’d like their beef flavored with just a hint of oak, or supercharged with the flavor of mesquite.