The best espresso will depend on your own preferences - some like their espresso bold and strong, others silky-smooth, and others full of flavor. The best way to find out what your preference is, is to simply try it!
Coffee Beans Used for Espresso
Coffee beans used to make espresso are usually of the Arabica Coffee bean varietal (Coffea arabica var. arabica) though Robusta coffee beans (Coffea arabica var. robusta) are also used in some espresso blends.
While Robusta beans are generally considered lower quality than Arabica, they are well known to produce a nicer crema and contain higher levels of caffeine. Because they're roasted so dark, the differences in quality between between Arabica and Robusta beans become less pronounced.
Grinding Coffee for Espresso
The grind size for making espresso is usually very fine, and may need to be adjusted for particular espresso machines (espresso coffee makers). The grind is actually key to an espresso - too fine of a grind and the coffee becomes overextracted or doesn't pull properly. Too coarse of a grind and the espresso is underextracted and watery.
Any good coffee roaster will know what grind to supply for your equipment, though some equipment comes with built in a built in grinder which is ideal. As coffee (and therefore espresso) is best freshly ground, you want to purchase whole beans and grind it just before brewing.
Espresso Machine Types
For steam-driven espresso machines the grind should be extremely fine because the machine doesn't have as much pressure to push the water through the tamped coffee grounds as a pump-driven espresso machine, which can handle a slightly coarser grind.
If you aren't sure which time of espresso machine (espresso maker) you have, here is a tip: if you put water into the top of your machine and then screw a lid down onto it, then you probably have a steam-driven espresso machine.
Espresso Brewing Tips
For more espresso tips see our detailed coffee flavor profiles of gourmet coffee and instructions on preparing gourmet Espresso Drink Recipes. For step-by-step instructions see Pulling A Perfect Espresso Shot as well as How to make a Latte.
For smart tips on brewing the perfect cup of coffee see our section on coffee brewing, and detailed definitions of espresso and coffee terminology can be found in the Coffee Terms. Also check out the World's Best History of Coffee.