Originally Posted by choddo

34 gets up hills easier
but has slightly bigger jumps between gears
And is probably a tiny bit heavier
and you’ll likely need a longer chain for it (by 3 links so might even get away with it depending on how long the current one is) but a new freewheel probably deserves having a new chain at the same time anyway

assuming both freewheels have the same number of cogs of course.