Hard to really compare these franchises.
Final Fantasy has been a whole different game each time, new battle systems, characters always change, stories different, enimies are different, it's not consistent like Zelda, it's much more difficult to mess up because people have to love the new characters and story all over again. It'd be better to compare Sonic or even Resident Evil with Zelda.
Me answering this question is pointless because I'll played pretty much every FF and I've only played like 4 or 5 Zelda games, so I'm too one sided to start.