Time to save this topic from the pits of stupidity. PCB Studios is by far a better choice to do Sonic stuff than either funimation or 4kids. The studio has a pretty good track record in terms of VA, often times being praised by critics in the review of a game. It would also be more economically more beneficial to Sega as well since PCB is based in California. From there, its time for my two cents.
-Sonic: Shiloh Strong. Has done characters with a very similar personality to Sonic (hot headed, cocky, strong sense of justice, disdains weapons, fighting style that combines speed and strength, always keeps his promises). Good choice for an older Sonic (at least 17).
-Dark Spine Sonic (or other "dark transformation that shows up): Yuri Lowenthal. Capable of showing intense anger and hatred in his roles or can play a super smart ass (Gig anyone).
-Tails: Colleen O'Shaugnessy. Everyone that complains that Tails sounds like a girl is an idiot since women are commonly used to play male characters less than 13 years old. Besides, Genis is very much like Tails in terms of character type.
-Knuckles and Espio: Crispin Freeman.
-Shadow: Derek Stephan Prince. Good at playing either "dark" or "cunning" characters. Oswald the Shadow Knight in particular is in a way, like Shadow (messed up past that colors his personality, cold, brooding, aggressive, quiet, slow to earn his trust but is extremely loyal to those who do, dangerous whenever said person is in danger).
-Amy: Kate Higgins or Stephane Sheh. The former is better for a younger, less mature Amy.
-Rouge: Wendee Lee or Michelle Ruff. Depends on what aspects of Rouge's personality get more emphasis. If her trouble maker smart ass aspects get more weight, then the later is the better choice.
-Omega: Jamieson Price. Playing the role of a big, red, angry, vengeful, violent robot is not much different from playing the role of a big, red, angry, vengeful, violent dragon.
-Tikal: Tara Strong
-Cream: Sandy Fox. Good at playing innocent, naive characters (i.e. Flonne, Marona).
-Blaze: Kari Walgreen
-Metal Sonic: Lex Lang. I envision Metal Sonic to be a megalomaniac, psycho overlord type.
-Egg Man: Michael McConnohie. Can play both comedic and serious characters.