1. Egoraptor: Brilliant performer in both comedic, and even serious styles (see: "That Damn Right Arm" on his SheezyArt page). His versatily and energy go almost unmatched in online voiceover. He's does a ton of non-"awesome" voicework too, which constantly goes overlooked by his critics and fans alike. At the same time, he's -always- working on projects of his own.
2. Kirbopher: Very smart actor and can deliver some incredible energy. I think his range is very limited outside of "average teen" and "tough Brooklyn accent", though I may yet be proven wrong. Sonicmega works a very similar style but with better range, although I consider Kirbopher the smarter actor of the two. Kirb would be in more flash animations and games if he were more proactive about pursuing roles. It's his own choice, really.
3. Hans Van Harken: I'm actually surprised you're not a fan. He has a very "old school" style approach to most of his work and influences, and is a -very- smart director. His range can be rather impressive too. I know full well that impersonations aren't everything in acting, but watching "Hans Van Harken does Family Guy" on YouTube makes it blatantly obvious: The guy can go.
4. Francine Louise: Raaange. You'll be hard pressed to find a more versatile female in amateur voice acting. Character ages from children to elderly, accents from British to Jewish to Slavic - she can pull these off. It's hard enough finding a female AVA who even -attempts- them. Her energy has really lacked in certain roles, I will agree, but if she's being directed well, that no longer becomes an issue. She's definitely capable of getting her energy up there.
I'm a HUGE fan of Faye Mata/PrincessAurora's voicework by the way. But once again, she hasn't been pursuing online roles heavily at all. Otherwise, she'd probably be EVERYWHERE. I suppose I'll need to play through Griswold 2 at some point, but Rebecca McCarthy's prior work has been very hit or miss for me. But if you want the very definition of flat delivery, look up any role of Katie "Voicegirl" Dehnart. Not... good. And she doesn't seem to even care.
5. Chris Zito is an AMAZING comedian, and there was a time when he was in -many- things. I might be waaay off in thinking this, but it seems in recent years that voiceover has become less of a priority for him, and I feel the quality of some of his more recent performances has slipped a little bit as a result. But still not enough to keep him from being the great talent that he is.
Cailen Denton. I'm... not sure I even know him. Was he the Green Ranger in Parody Rangers 2? That was actually my least favourite performance in the animation due to it being so underplayed, and the poor mic positioning only hurt it more.
But the bottom line is: The VAs who pop up in the most Newgrounds productions will remain those who dedicate the most time and effort to their craft. Constantly practicing, auditioning, looking out for new roles, improving and marketing their demos to the right crowds.
Having natural talent is a big help of course, but VAs who aren't yet established, and truly desire to be, can only look to themselves for not taking these steps. There's a ton of room for more vocal talents on NG, so blaming those who've already worked long and hard for their noteriety, is simply meaningless.
D-Mac-Double
"They emphasize on high-end equipment over actual acting skill." Well, that's blatantly not true. Also, if anyone deserves to be in everything, it's John Mondelli.
<a href="http://www.youtube.com/watch?v=776vqkl9MMQ">http://www.youtube.com/watch?v=776vqk l9MMQ</a>
Will add a lot more when I'm less busy, as I've been meaning to get back to you.