Asterix is the titular character of the French comic book and film series. Although small in stature, he is a capable warrior, using both his keen intelligence and the strength-giving Magic Potion to turn the tables on the Roman invaders.
Personally, I think that Lee Payant, Jack Beaber, Paul Giamatti, and Ken Kramer are the best voices overall. But if I had to pick a favourite, I'd have to go for Jack. He sounds the right size, and manages to convey the aggressive-yet-clever warrior without sounding too heroic.
Of the others, Sean Barrett sounds a bit light (even for someone of Asterix's stature); Bill Oddie is decent, but too squeaky; Henry Winkler has the right voice, but slightly awkward delivery (and the material he got didn't help); Craig Charles has good comedic timing, but it's distracting to hear Lister's voice coming out of Asterix; and Les Clack's Welsh accent takes a bit of getting used to (although, to be fair, it's probably more accurate than if they'd given him a French accent).