It's hard to decide which sonic is the best.
Neo-Sonic is somewhat out of character with lightning ball attacks and shoryuken style uppercuts, Cheap assist attacks and Super Moves, And a near impossible AI.
While MugenHunters Sonic is similar to most SNK Fighters in terms of gameplay and control, The moves are accurate to the Character and its ballanced too, Recomend this.
Last but not least is Claymizers Sonic, Which is based off a slightly Modified MVC style, The SND that usually comes with it sounds like its being recorded from SSBB and not ripped, The sprites are decent and he plays fine, He also has a move similar to shun goku satsu Where he turns into Dark Sonic, but instead of taking super power, It Takes health away, It's pretty good altogether.
My advice, Get Claymizers Sonic, He's easier to find then Mugenhunters, and is easier to control for new players.