They both are good depending on your other heroes and the way you like to play the game.

Honestly lemme give u the unbiased opinion(since i use madara 5k), both are good, in their way of playstyle, and both have different synergy depending which ninjas you have, now keep in mind, madara 5k completely denies any buffs / mysteries from being pulled or had and doesnt get chased pretty much like edo itachi, while edo itachi just denied shields, buffs, have a reflect mirror for every round starting and puts ur target into a "dream" state, which is basically a sleep 2.0, with that said, i think it comes really want and what ninja you have, i think meta is what you make of it, in this case with top 10 have mostly, team wise, keep in mind also, there's a counter for every ninja used in this game, if you're looking to just have fun, just go with ur favorite ninja from the 2, if ur competitive, i'd say any of them is good, and have good kits.

Man the problem is that both of them can serve position 1 very good which in this case naruto sosp or minato ..they will both combo and they will do whatever you need as a 1st support ninja (position 2).

this is what books say but if you are having minato or edo diedara as position 1, then get 5k madara and if you have naruto sosp get edo itachi.

Other thing you need to put in your consideration is the 3rd ninja you are having. for example having susano kakashi in your recruited ninjas that means you do not need edo itachi right now and he could wait.

finally, for my opinion go for 5k madara especially if you are faster than most of your bracket. Edo itachi most benifit is to make you have a fighting chance against AGK and Edo heruzin teams. but 5k madara is more tactical with interrupting mysteries and repulse chase and stealing chakra which can be very helpful.