My initial ideas are always Spontaneous. But growing that original idea into something truly special requires a long, thought out adventure. In the end, both are fun and exciting but nothing gets my blood pumping more than when that first idea pops into my head and I have to get it out as quickly as possible.
Most of the time a spontaneous thought pops into my head, but it's the execution of it that takes a lot of planning and thinking out. It's extremely rare for me to have a spontaneous thought and set to work with it without really thinking about what I'm doing, almost by instinct.
There's also are a few times where I've spent a lot of time planning and thinking about something, usually searching for a solution to a problem, and I will quite suddenly realize what to do and set about doing it. Of course that usually comes when I'm doing something completely unrelated (even when I'm about to fall asleep) and not thinking about it at all.