Tough when you put versus in there.
I have Ozone 5. If you're a novice to an experienced user, either way, right out of the gate Ozone 5 works. Easy to get helpful results. The more you work with it the better it gets. It's very intuitive. So you'll get your money's worth for sure. The ample presets are a helpful starting point.
I'm just getting in to the Melda stuff now. BitFlipper helped throw out some reasons why it's powerful stuff. I've actually worked with some of the Melda tools now and can hear an exciting and extra special quality as a result of early experiments. But, the interface is taking some time to understand. And the depth of the tools seems like I'm just peeking at what's ahead in learning them. I think users need to be more experienced overall to take advantage of quite a few of the numerous features of Melda tools.
So if you're totally all in to audio engineering I would say both, or perhaps Ozone 5 and a selection of the tools from Melda. If you had to choose only one I'd say Ozone 5 because it's a slam dunk. And, if you're aiming for only the ultimate in best results you might want to go for Melda only instead, but be prepared for a slower ramp to understand its features and capabilities.