NudiLover, I'm in the same situation as you are. Because most of the dive buddies I've drawn have been real jerks, I have more on the negative side than the positive. But on my last dive experience, I was the only diver at the resort, so I got to do six dives with a dive instructor! He was awesome--thoughtful, helpful, tactful, and always ready to go the second mile. I felt totally spoiled!
On the negative side, here are some things I've really hated in dive partners:
1. The fellow who bragged about his hundreds of dives. It was a night dive, and Mr. Expert silted up the bottom so badly we couldn't see a thing. Back on the boat, he loudly accused me of having done it.
2. The guy who didn't listen to instructions from the divemaster. I was faced with choosing between sticking with the buddy (and going against the DMs instructions), or staying with the DM and losing the buddy. I stuck with the DM, and back on the surface the buddy complained that I didn't stay with him. (Yeah, I reminded him of the DMs instructions, and he kind of hushed up). I found it interesting that he never made any effort to stick with me.
3. Which brings me to the third point. Most often, I've ended up with dive buddies who expect me to follow their agenda. I end up with the responsibility of keeping track of them while they do their thing.
But having read this thread, and a few others about dive buddies, I can see that some of these situations could have been improved by more communication at the surface before the dive. As I've usually been the more inexperienced diver, I've been kind of reticent to take the lead in pre-dive communications; but from now on I shall do so, if necessary.