Is courage a virtue or is is simply the ability to conquer fear?

These options needn't be mutually exclusive, right? A common definition of virtue is "a habitual disposition to act in accordance with the good for its own sake." If courage is the ability to conquer fear, and conquering fear is good, then assuming that the ability is a habitual one and not some kind of flash-in-the-pan inspiration, the answer to your question would be "both." Aristotle counted courage as a virtue, and pointed out that virtue is found in the mean between the opposed extremes of deficiency and excess. The ability to overcome fear, if carried to excess, would not be the virtue of courage, but rather the vice of rashness.

I've noticed a difference between some eastern and western approaches to philosophy. Some eastern traditions seem to emphasize personal serenity and enlightenment through meditation, while some western traditions emphasize wisdom through curiosity, questioning, and thinking. My question is, which is the higher human good: serenity or wisdom? More concretely, which image represents the best in humanity: Buddha meditating or Socrates thinking and conversing on philosophic questions?

I'm thinking the best in humanity would encompass both; don't you agree? Serenity seems eminently compatible with wisdom, and some interpretations of Aristotle's eudaimonia (flourishing, roughly) characterize it as serene but active contemplation of wisdom. (I'm grossly oversimplifying on eudaimonia , but it is a well-known conception of the highest human good that accommodates much of what you suggest as opposed.)