These are pretty much the main dubbing companies that are still around in the US.
Funimation
Viz
4kids
Aniplex/A-1 Pictures
Section 23
Funimation has sued 4kids over Yugioh which caused 4kids to file for bankruptcy. Funimation now uses 4kids to market shows like DBZ Kai and any other funimation dubs on other networks. So in a sense Funimation owns 4kids.
Viz is the strongest dubbing company other than funimation. It is hard for Funimation to try and bully them as Viz has the money to fight back. Viz is also known for many of its anime and manga like bleach, deathnote, naruto, one piece, ect.
A-1 Pictures I would say is third on the strength list it has many anime that have been made popular by adult swim.
Section 23 is a hodgepodge of other anime companies that decided to escape debt by ending their old companies and forming a new one. Channels like the Anime Network are owned by them as well as many old anime and some new ones like Highschool of the Dead. Their big problem now is money. Court costs to try and get the rights to Evangelion for the live action film that they have already paid in full is staggering I am sure. Not to mention Funimation brining up a 8 million dollar suit against the company for anime purchased by ADV back in the day that ADV/section 23 says that they have paid in full. Section 23 also has some connections with the Warner Bros company.
Funimation seems to have a habit with trying to destroy any company that is having an issue with a japanese company. I don't know if they are intentionally trying to do this. However the way that it is looking Funimation could be charged with a Monopoly if they keep absorbing or eliminating other dubbing companies. Funimation is also known for having the rights to the Rebuild of Evangelion films 1.11 and 2.22. It wouldn't surprise me in the least if they are trying to put Section 23 under so that they can have a chance to buy the rights to the Evangelion series and a Live Action Film.
This cosmic dance of bursting decadence and withheld permissions twists all our arms collectively, but if sweetness can win—and it can—then I'll still be here tomorrow to high-five you yesterday, my friend. Peace. —Royal Tart Toter.