Just to be annoying because I majored in Psychology-

If a sub does something wrong and the Master punishes them, it is not negative reinforcement. Negative REINFORCEMENT reinforces something. The object of punishment is the opposite- to discourage a behavior. Negative reinforcement would be like saying- you don't have to do pushups today if you eat your broccoli. What we are talking about here is positive (and perhaps some negative) punishment. Positive means giving something- negative means taking something away. Positive punishment is something like a spanking, and negative punishment is something like not being allowed to watch TV for a week. See the difference?

ANYWAY- back to the point:

I think that both are important for me. Obviously- as a sub, I love rewards, and if it is a good reward I would work very hard to please my Master. On the other hand, I have a tendency to be fiesty and not well behaved in prior relationships, whether because of resentment or what have you. I think a good spanking or slap is a good reminder to behave and treat your Master with respect. However, personally, I am more unhappy to know I have displeased my Master (or in the opposite case, happy that I pleased Him). To me, these are the best encouragements and deterrents- however, throwing in a few rewards and spankings is also a good way to spice things up :-P