The correct answer is that it depends on what you're trying to do. That's why crossbows and longbows existed along side each other until firearms made them both obsolete.
Crossbows have more power, but the fletching on an arrow causes it to wobble less, which evens out the range and accuracy, and for piercing weapons in general accuracy is more important to kill potential than power anyway. An arrow to the vitals will immediately kill you, and a bolt to a non-vital area won't immediately kill you. Arrows also have plenty of power to penetrate most armor, so overall power, accuracy and range are all moot points.
Basically it just comes down to a few guys firing rapidly vs. a lot of guys firing slowly. A group of longbowmen is likely to have been well trained, which has other side effects such as increasing loyalty and morale, while the crossbowmen will be easier to replace if the war drags on. Also, crossbows are more expensive than bows, while arrows are more expensive than bolts, again favoring bows in shorter conflicts and crossbows in longer ones.
I chose bows in the end, because they're overall slightly better at first, and if the war drags on you can replace them with crossbows as you go.