Doesn't really matter to me, as long as it is fun and addicting. Although, I voted for Castle Defence + Tower Defence
I like the fixed path, but there needs to be something to do, or a fast forward button, because in the early stages, waiting for the easy creeps to stop coming is boringg!!!
I chose fixed path as my primary choice. The build your own maze/open field is my 2nd. The PvZ castle defense type is definitely a distant 3rd.
I chose the fixed path option because it's the easiest for a casual gamer who wants a pick up and play option. PvZ is in a category of its own because of the large hype it had due to the online version and the clarity of the graphics. (I own PvZ by the way).
What would games like Biodefence and Space Station: Frontier go under? I think of them as TD games but maybe they're more like RTS games.