It's about even, I think. Probably slightly in DK's favor. DK B-Air rips Ivysaur to shreds offstage if Ivysaur can't reverse Razor Leaf in time to be able to protect herself with B-Air.
DK's tilts are stupid, but it's not hard to grab him (for Ivysaur standards, hah). Ivysaur F-Tilt does a number on him, and it's pretty easy to get him in Bullet Seed (any shielded tilt gets punished, really, and Ivysaur can do it to a DK from below, too).
Ivysaur can actually edgeguard the **** out of DK, too--He gets punished badly (Bullet Seed, U-Air, U-Smash at times) for coming from above, he can't come in level because of B-Air's range, and coming from lower is asking to get N-Air or D-Air spiked.
It's big on momentum. They're both pretty safe in general if they do their spammable moves, but when someone messed up, they get punished badly. It's about even, though.