In Stoicism, "passions" were things like lust, depression, malice, jealousy, as well as more run-of-the-mill things like anger or fear. While Stoics did believe (most) passions were bad because they produced (physical) imbalance, there was one good passion: watchfulness. So, not all "passions" were bad. Furthermore, the "passions" are just a subset of all the "impulses" that a soul can produce. The soul can also produce good "impulses" (called the virtues), as well as ones that are entirely indifferent (called "adiaphora"). The wise person will choose a proper lifestyle (mental exercises, going to the baths, reading, moderation) so that his soul is not dominated by passions.
In Aristotle's conception, instead of "passions, virtues and adiaphora", the soul has "passions, capacities, and states". Passions and the capacity to feel them are neither good nor bad. They just are by nature. Virtue, however, is not natural, but requires a choice, and becomes a state of the soul if we choose it. In both systems, the rational mind must choose virtue.
If you want to read more about Aristotle -- but don't want to slog through Aristotle himself -- the big daddy of English-language Aristotle scholars is Jonathan Barnes. He wrote a great introduction to Aristotle in Oxford's "A Very Short Introduction" series.