The short answer
Arabica and Robusta are two different coffee species. They tell you something about the raw material, but far from everything about how your coffee will taste.
The bean type is only the beginning
Arabica is botanically known as Coffea arabica, Robusta as Coffea canephora. The National Coffee Association lists both as the major commercial groups. But how the coffee ultimately tastes is only decided during processing, roasting and brewing.
The two also grow differently: Arabica grows at higher altitudes, ripens more slowly and is more delicate. Robusta copes better with heat and pests and yields more. Hence the price difference — and hence also Robusta's reputation as the lesser bean.
100 percent Arabica says nothing about the flavor
The label "100 percent Arabica" only describes what's inside. Whether you'll like the acidity, aroma and mouthfeel isn't determined by that. A blend with Robusta can just as easily be exactly your style.
So don't rule out either species from the start. Try the finished coffee and tell the shop how you drink it: black from a filter, as espresso, or with milk. That will get you a fitting recommendation faster than asking about the bean type.
Italian espresso traditionally includes a share of Robusta, and that's not cutting corners in the wrong place. It adds more body, a longer-lasting crema, and the bold finish many people love in espresso. A pure Arabica blend can be too delicate for that.
On one point, the bean type really does settle the matter: Robusta contains roughly twice as much caffeine as Arabica.
