Well, I have two mustangs (adopted from the BLM) and a 1/2 Appaloosa/1/2 Arabian. To my mind, the mustangs have never been "hot tempered." They were skittish when I first got them, but settled down really quickly. The Arab X is more moody than my mustangs (but that could be his age - he's 22). He's a very solid trail horse - doesn't spook at anything. My mustangs aren't skittish, either. I board a friend's Morgan, and he is the flightiest thing I've ever seen - will spook at a cloud floating by. I think it really depends on the individual animal. I've seen some very "hot" arabs, but I've also seen some that are just wonderful. That said, my mustangs are definitely my favorite. They are very friendly, come when I call, follow me like dogs, and love to be petted and give kisses. But that's just my feeling. You really need to look at each individual horse, figure out what it is you want him for, and see how he responds to you.
Liz