Greek has more moods. Each of which have a load of random functions.
Greek also has nouns that have their own declination (for example the word for king - Βασιλεύς).
That being said, Finnish has what, 20 cases? They lure you in saying you won't need to learn any prepositions because there'll just be a case for that, but then they also have more prepositions than any other language I've come across.
I generally think conjugating verbs is more practical than putting auxiliaries all over the place.
Also, Japanese grammar is... manageable, compared to Indo-European and especially Finno-Ugric languages.
Come to think of it, I think each type of language has its own difficulties. Like how in Arabic you need to gender-switch a lot but Arabic grammar in general is really simplistic when you look at it closely.
Hindi/Urdu requires you to conjugate verbs differently based on the subject's gender. Even in the first person. Actually the nouns get left alone for the most part (or at least pronouns do), but the verbs... so if I get a male friend to translate something into Urdu for me I always need to double check if he did the verbs like he would say them, or like I'm supposed to say them. It's a pain.