Only agree that Mashima draws women better but that's also because he's a literal coombrained artist and self-admitted to it just like Hellsing's author/artist. Everything else Oda does better, particularly background art, scale, etc...though I have a huge issue with Oda's women/female designs being very much a template of three or four very basic designs:
- skinny/normal with hourglass body shape
- fat and boxy with a more rectangular figure
- the "muscular" women who are just skewed between those two main ones like Boa's tribeswomen
That and Oda can't really into muscles for shit unlike say Toriyama. Still would say he's overall a better artist then Mashima.