first of all, even if they are both babies they still have nothing in common.
One wants to take over the world, one wants to be a baby, one is yellow, one is white. One can do flips and is very capable in any type of battlefield while one would cry for their mommy.
But since you wanted to know, I'd say Stewie Griffon
Maggie is really the daughter of Kang (or Kodos) and has super powes. That was only a Haloween special? It doesn't count? Stewie is way better more storylines are based on him, maggie is in alot of jokes but not really an instigator except when she shoe Mr. Burns. Plus Stewie has an english accent
Yeah but Maggie shot a Italian-American with a machine gun.Shot Mr Burns with a pistol.Saved Homer with cuteness or with guns loads.And did you see all her guns on the episode when Bart and Lisa banned guns(Mr Blasty is awesome by the way)and is just awesome and could sniper Stewies big fat son of a bit*h head easy.
Anyways, Stewie. Hands down. Maggie's just a typical toddler, but Stewie seems to be an utterly snobbish 19th Century Gentleman accidentally put into a baby's body.