Usually, the voice actors that are considered to be better are typically the ones that have been doing it for a long time. Some have been in the anime voice acting biz since the mid-80s (like Tony Oliver, for instance).
In my experience, Bandai and Pioneer/Geneon tend to get the best casting, followed closely by ADV's recent releases, Funimation is a mixed bag - some are well-dubbed, like Fullmetal Alchemist, but others are closer to Dragonball Z's cheese factor - Manga Entertainment and ADV's old releases are about neck and neck in overall suckiness, and Media Blasters and Central Park Media have some of the absolute worst acting I've ever seen...erm, heard (and sometimes the original Japanese acting wasn't so hot either; Weiß Kreuz, anyone? At least the outtakes were funny). I also don't find it a coincedence that that is also pretty much the order that quality DVD releases go in, with Bandai and Geneon putting out the nicest-looking releases and CPM and their ilk putting out DVDs with crappy transfers.
Personally, there are two problems with your general crop of anime voice actors - 1) it's a very small pool that gets pulled from, so you have actors that are seemingly everywhere, and as a result seem very overplayed, and 2) the acting has a tendency to get a little on the hammy side, but this is the result of the direction, not necessarily the actors (although it certainly could be a combination of both). I think a better solution would be to hire out casting directors from the major networks and hold the casting to the same level they expect from the other series they work on, so at least the quality of the actors would be more akin to what you'd find on regular TV.