I don't really think there is any point in comparing the two, to be honest. Generations the last game in 4th generation of Monster Hunter. Therefore it must keep the old style of gameplay while getting ton and tons of contents. Monster Hunter World is the start of a new generation. It is like comparing Pokemon Black 2 to Pokemon Y. You really only compare because you want both games and must pick one.
It basically boils down to content vs gameplay at that point.