I miss the option "both". They have their pro's and con's as everything in this world.
RTB (I know it as ATB, btw) is more challenging. You don't have much time to think about a strategy, you just beat the crap out of the enemy. And also, it's quite difficult when you think about it too long and then the enemy attacks before you have a chance to attack. Also, I've had that so many times: I wanted to attack an enemy and while I waited for my character to act, the enemy killed him off. O_o So then I have to act fast again, so that the enemy can't kill off the other characters. That makes the game interesting.
Yet, it lacks strategy. You just attack every time. I mostly don't use magic because I had to think about what I should cast at the enemy. I normally just use Icega then. xD" Ice is always good to damage the enemy. But I don't think about what I'm doing - I'm just doing it.
CTB is more about strategy. For example in FFX I really thought about what I'd do and when I finally realized that I saw that I can see who's up next, I based all my strategy on that. (I couldn't have beat any Dark Aeon without strategy ^^") It's quite great when you then beat the enemy, because you know it was your mind which did it, not your strength.
What it lacks is challenge. It gets boring soon. To be honest, when I was thirsty inbetween a fight I just stood up, thinking "pah, he can't kill me because it's my turn", got something to drink for me, drank something and then played again. *yawns* Boooring~

All in all (I'm talking too much today O_o) I choose... both! =D Although it's not in the poll. xP