Geno didn't have much personality and was of questionable use to the plot (despite coming from the Star place) but he was fairly useful in the party (so long as the other character was the Princess). I think Mallow has a stronger personality and was more important to the plot, but wasn't as useful in the party, since he wasn't as useful in the "White Mage" roll as was the princess, nor did he have as powerful attacks as, say, Bowser.
I LOOOOOOVE Flying Omelette!