Malinois temperaments REALLY differ from line to line. Show and working malinois have such a split these days. Show malinois can be shy and "freaky," shy-sharp, noise-sensitive, etc. Working malinois can be very aggressive with excessive drive problems and alot of working sharpness. Getting a good malinois depends on where you look. Belgians in general are a difficult breed to get into because it is definatly hard to find a good-tempered one. They will have a good recall if taught well enough but shouldn't be trusted offleash -- malinois especially can be very prey driven. I've seen anything from a moving cat to a moving child set a Belgian into drive, and they will chase what they see, and some will try to catch what they see. You always have to remember when you have these dogs that you are responsible for them -- they are high energy, high drive, intense, and many of them are unfortunatly aggressive. These are all combinations for disaster if the dog isn't properly controlled. However these are also traits you can mold into a good working dog.
High drive Belgians are not the easiest to train for agility believe it or not. My dogs are high drive, I've trained with high drive Belgians. I've never met one that didn't have some form of working sharpness. Basically this can be as small as biting the owner when in drive to full out being handler aggressive when in drive. But I must say the biggest challenge is controlling the dog on the course. They will often choose their own course, sticking mostly with the contact equipment, especially the TUNNEL. I still have a hard time getting Visa to go over the jumps -- her eyes are glued to the contact equipment. When I first started with her, she would literally run through the tunnel back and forth ten times in a row before heading to the A-frame and running up and down it ten times in a row. My co-breeder had one dog who did the dog-walk four times in a row back and forth and managed to miss the contact every time LOL.
Belgians are AWESOME at agility because they do have the drive, the intensity, and they do want to work for you -- plus-sides are the speed and agility and the amount of physical control which definatly tops the border collies who tend to knock bars due to jumping too soon. Alot of serious competitors switch to Belgians because they definatly are good at the sport. But the amount of work it can take to get there is a turn-off for alot of people. When I first started classes I was placed in a group with three other groenendael. They called us the "impulse control group."