One of the more salient experiential differences between responding and reacting is the difference between presence and habit.
The value of habit is the mindlessness. We don't have to consider context, larger purposes, change or options. Habit is efficient. We just react in business as usual. And with good habits, reacting from them works. Reaction is attractive when we crave a more predictable world than the one that actually exists.
Presence is mindfully responding where we stay present both to the situation and any habitual reactions that emerge. Presence diminishes the gravitational urgency of reactions. We move from mindless reaction to responsiveness in possibility space.
Important to note that responding and reacting are distinct and form a continuum, making it possible for actions to share the synthesis of each. The two also intersect when we mindfully and responsively create new skillful habits that become new useful reactions.
The responsiveness of presence makes it possible to act out of compassion rather than self-interest, even in the same action and outcome. To the observer, the same action as responsiveness could look like reaction. The difference between reacting and responding is in the quality of attention and intention.