Hungary was a bad choice to expand into - the plains were too large, too open, and too Christian. They'd have had energy to do better elsewhere if they'd snatched a bit of Hungary's frontier, demanded tribute, and stopped.
Alternately, if they somehow lucked their way into an early capture of Vienna, holding Hungary would suddenly cost them much less, and open up many other options. Not so much options in Germany, but the reduced overstretch could pay off on other frontiers.
That said, there weren't too many options lying about that would have been simple to grab. What do we mean when we say "maximum"? Largest territory? Then the easiest way would be the Ottomans exerting their precedence in the Arabian interior and upper Nile. Which would be costly wastes of effort given the technology at the time.
Limiting things to what I suspect was meant, in rough order of ascending difficulty: The Trucial States or eastern Caucasus would be the easiest. After that the Mezzogiorno, which would be quite complicated to arrange. Then the rest of Italy or Morrocco. Then the very challenging foothold on the Iberian Peninsula. Finally, Persia.
Alternately, there's the colonial option. The Ottomans launched a surprising number of ambitious maritime adventures between 1500 and 1700, from North America to the East Indies. Conceivably, they could have pulled off something extraordinary. It's probably easier than holding Persia alongside its OTL empire (not that that is a high bar!).