There should really be a mixture of these two game modes. Simultaneous mode is great but gives an advantage to players who can time a double move. That is probably why I, and most players, prefer turn based mode. It however takes forever to play turn based in the beginning of big FFA games when there still is 8 players. In my opinion, there is however no need for turn based at this point? Instead the first couple of turns could be played in simultaneous mode before switching over to turn based mode.
Maybe an option for the person creating a game, e.g. "number of turns simultaneous".
Or maybe a more clever function that detects if any players can reach each other within two turns -> switch to turn based... (this information, that no one is close, may however be abused on some maps with fog wars...)
Playing the Fibonacci-map now, could probably have 5 or more turns of simultaneous, but instead it will take a week in-between turns taking a minute or two to actually play...