I'd say it'd be just about even, with Banjo eeking out the victory. Kirby might have a bigger bird but he has a smaller frame to swing it around. Banjo on the other hand has more experience.
*HEETAAN*
SFX from Banjo-Tooie
MURI MURI MURI
MURI MURI MURI
"Muri" roughly means "not a chance" here; very similiar in vibe to Jojo's "Muda".