I'm not a huge monitor fantatic, but here's my $.02...
Don't know a huge bit on ackies, but I always hear good things about them and how they have relatively better dispositions than most other varanids. They also require slightly less space. The only downsize is that they are initially more pricey than most as well.
I've kept savs before so here's my spiel on them...
First of all, their temperment can vary greatly with diet, method of feeding, amount of human interaction, and most importantly, individual personality. I had one named Titan, and he was a puppy dog. Others can absolutely terrors.
I personally feel that part of this is greatly caused by diets primarly of rodents and rarely anything else. While not wanting to turn this into a heated debate on sav diets, I would like to point out that approximately only 5-10% of a wild savs diet is rodent prey. I would also like to say that savs (like many animals) have whats called a "gorge factor"; In other words, in nature, they do not come across a hefty meal every day so when they do, they gorge themselves because they don't know when their next meal is (which could a week). [FYI, my phrasing can be misleading; they really have no choice in this matter; they're simply acting on instinct].
Now in captivity, when they're given a rodent every day, they act the same way, feeding with such vigor which prompts the owner to feed them more, thinking they're still hungry. And of course, its so much more fun to watch a lizard eat a mouse than it is to eat bugs and canned food, so the end result is a very obese monitor that dies prematurely from kidney or liver ailments.
On top of that, owners usually feed the monitor in its cage, because they think its mean. So just like some snakes, the lizard associates the opening ot the cage with food, and in a roundabout way, actually does become cage-aggressive. So from these scenarios spawn two false myths: A.) all savs are mean and b.) savs must be fed rodents. Both are quite untrue.
Now I'm not going to tell anyone not to feed their savs rodents (although I never fed mine any and he turned out great). However, I do suggest feeding them rodents in much moderation, perhaps one once a week or even every other week.
Back to the topic....IMO, savs are a great beginner monitor as long as you prepare for their adult size. A custom-built enclosure is probably the best route. Feed them right and spend time with them, and you might end up with a bg lizard that does tolerate occasional handling.
[Z-trip, stand down. I already know you're going to declare that feeding savs mice will kill them. I've already addressed the issue and I didn't have to use all caps locks to do it. Your stance on the matter is dually noted.]