It seems the only difference is that Tia, Slime and the puppet girl may be available from account creation. It think that the other versions required you to get a character up to the point in the story there that particular character joins the team to make a character of them.

Each one is basically an advanced counter part to one of the first 3 that is harder to play(Sieg > Tia, Eir > Slime, Dainn > puppet girl) and aren't really recommendable to beginners. For instance, Tia is a rouge like character, and is much faster than Sieg in every way, but is extremely difficult to control for the same reason. Add to the fact that she has less defense and a newer player could easily get them self killed with out even knowing what they did wrong.