Well, it depends hardly what type of flying you enjoy the most: Is it longhaul? Go for Ethiopian.
Is it short/middlehaul with mostly turnarounds and some layovers? Go for FZ.
However, the salary is much better at FZ than with ET and i think Dubai is a 'bit' better to live rather than Addis.
But when it comes to rosters, FZ doesn't sound appealing either.
From my own preference i would take FZ but once again it's very important that you make sure for yourself what type of flying suits you more.
I'm done with the sandpit but there are still people enjoying it there.
Good luck with your decision.