OK, HERE IT IS IN A NUTSHELL...
Both are excellent natural energisers, far exceeding the potential of caffeine. Both come from the Amazon, the worlds richest eco-system.
* Yerba Maté is a leaf - steeped to produce an infusion (tea).
* Guarana is a a fruit (seed in a berry) - the seed is ground and consumed whole.
Because of this difference, Maté is a more gentle tonic, whereas Guarana is a stronger, more intense energiser.
An excellent enerising effect can be produced by combining the two: adding a small amount of Guarana to a Maté tea, which would help balance the intensity of Guarana with the gentle, sustained effects of Maté.
Tribal Trading has produced its famous "Triple-Strength Energy Tea" based on that principle - a delicious combination of Organic Maté, Guarana and Acai!
For a bit more info - read on...
The world’s rainforests are just beginning to be discovered as premier supply sources of high quality, wild-crafted herbs. Many of these herbs are energizers that have been safely used for centuries to combat stress and brain fatigue, to counteract depression, and allay hunger during dieting.
The active constituents in guarana seed have been found to not be caffeine as was originally thought, but a related substance called guaranine. The two substances are quite similar in the laboratory, but authorities on xanthines and stimulants make a distinction between caffeine, guaranine and mateine in their activity. Guarana and mate are what is called “cooling stimulants,” releasing revitalizing energy to the body as tonics. They are naturally-occurring, food-source substances, with chemical similarity to caffeine, but with important and subtle differences in the way they work in the human body.
Caffeine is a short-lived excitant that is heating to the system. It delivers its punch immediately to the body. In long term, high dosage amounts, like those supplied by several cups of coffee, the heated hydrocarbon by-products can create irritation, indigestion, and nervousness. People who have difficulty with caffeine seldom have problems with guarana and mate.
Guarana berries are rich in natural oils that combine with the guarana to block rapid absorption into the body. (This effect is very noticable when guarana powder is mixed with water as in a tea. It does not dissolve easily, because the oils are holding it in check.) Its stimulant activity is released slowly as the oils are broken down and digested, allowing for natural time release effect over many hours.