Short answer: It depends on what you're using it for
Pure leaf yerba mate is great for coffee makers and French presses. Leaf/stem yerba mate is great for mate gourds and tereré.
Pure leaf yerba mate is a great choice for the coffee maker
A pure leaf cut has little to no stem in it, and very little powder as well. It's a nice choice when you're brewing yerba mate in a French press, espresso machine, or coffee percolator. It's easy to work with, and it makes a strong, bright cup of mate.
Choose a whole plant cut when drinking mate traditional-style
I prefer leaf/stem yerba mate whenever I'm preparing a traditional mate or tereré. Also known as yerba mate con palo (Spanish for "yerba mate with stem"), traditional whole plant yerba mate contains stem and powder as well as leaf. Its flavor is milder (suave in Spanish) than pure leaf yerba mate. The stems add a subtle roundness to the flavor, while the powder lends a frothiness that some people compare to Japanese matcha tea.
Whole plant yerba mate contains about 10% less caffeine than pure leaf yerba mate, but whole plant is actually higher in antioxidants. Because whole plant yerba mate uses more of the harvest, it is more ecological as well as economical.
