They're different, but I generally lean towards being an improv heavy GM. I like turning up to a session with a folder full of NPCs and a starting point and seeing where the players go: I don't know who killed Duke Fluffykitten, but I know when the player's assumption needs to be wrong for a satisfying session (generally when they accuse the butler).

It's not that I dislike being a player, there's a fun to be had with coming up with a course of action that the GM is on board with. But it doesn't have the hectic energy of five players all trying to pull the game in different ways and the challenge of trying to balance everyone without reducing anybody's fun.