The more I learn about monitors, the more I learn that to be quite honest, there really is no 'starter' monitor. Ackies are considered starters because they are small. Though they are fun and energetic. But their care is just as intense as any other monitor.
The easiest monitor you can get is one that's captive bred (another reason why people say go with Ackies) because you have less of a chance of getting an already dying animal.
That being said, I don't know what the next 'level' monitor would really be. An argus is mean, but generally found to be all bark and little bite. They just want food all the time. And they are also one of the most active monitors out there. Watch the video "an argus afternoon" on youtube, how cool! But I don't know if I'd recommend them for a starting monitor. It's what I want, but I'll probably get an ackie first. These guys get big and like I said before, they don't tame down.
If you don't mind an animal that will never be tame and you don't mind feeding something huge lol an argus is quite an active and crazy one. There are probably others that are better, but that's the one I know.
It seems like monitors are either super shy, super aggressive, or blobs.LOL! I know there are exceptions of course.