Threads like these are completely meaningless. It just turns into a massive pissing contest.

This is like apples and oranges.

The difficulty of a language is an individual thing, based on your lingual (and cultural) experience, and which linguistic topics you are most comfortable with.

For some, the completely different mindset behind Russian, Japanese or Arabic might be a massive setback, for others it's the huge set of phonemes in Abkhaz, Ubykh and !Xoo, and for yet others, it's the cases in Finnish (though this is less of a problem in practice; Finnish is extremely regular, and the 'cases' are merely semi-fancy equivalents of prepositions; though, like Russian, Finnish has a completely terrifying verb system), and so on.

tl;dr: Pointless topic with a pointless question to which there's only a subjective answer. Go to bed.