I don't see how either extreme is possible. You simply HAVE to have both. I'll assume this is directed to GMs more than players, because players absolutely need to come up with things as the GM present them obstacles and as such they'd all be the second type. So with that.

You simply cannot start an adventure without the appropriate amount of planning. As a GM, you have to know what people the characters may interact with, how the world works and so on. Without that, there is no way to know how the world will respond to the player's actions, and the players is the one thing the GM can never control. Hopefully.

On the other hand, as I just said, there is no way one can control the players, so the rule there is pretty much "do not". As such, one simply have to be ready to be spontaneous, as there is no way one can plan every single detail. Sure, one can have a pretty good idea of what one would like the arcs to contain, but one should be ready to adapt real soon.

So, yeah. You simply must have both. Nobody can roleplay with only one or the other. Or have I plain failed to understand the first post here?