Ozymandias doesn't have ANYWHERE near as many intellegence feats as Luthor... mainly because if you stacked up every issue of watchmen, compared to every DC comic Luthor has appeared in, it wouldn't even be comparable.
The Watchmen Universe is way, way, way more realistic than the DC Universe. Ozymandias may be the smartest person in a world that's basically our world, with a few key changes (Dr. Manhattan, the presence of unpowered costumed heroes), but that doesn't mean he could handle things like... teleportation, time travel, boom tube and other New Genesis/Apokoliptian technology, biological research like it's done in the DCU.
Luthor wins pretty easily. it's impossible to compare the two.
well, seeing as how the battle states "world's smartest man," I assumed it was Watchmen Ozymandias, mainly because Apoc's manservant Ozymandias is an idiot, and would never be put in a battle for who's smartest.