All types! However, it does come down to personal preference as you'll quickly start to learn as you work more and more with your own machine. It all comes down to the smoking experience you love most -- some people prefer smokier flavors, while others are big fans of more traditional "grill" flavor. For example, if you are smoking a brisket, you might lean towards an oak or mesquite pellet. As with everything else in life, the best results can be found when you combine different woods for their unique tastes. You might find that a 50/50 mix is your favorite blend -- one for meat, and one for vegetables! Another thing to consider is the level of smokiness you're looking for. The last thing you want when cooking home-made burgers is a large amount of smoke flavor, so stick with traditional wood pellets that don't have too strong a taste or aroma.