I wanted mine in the middle before I got the game, but once I saw my current map I loved the position. It's just to the left of the train station with a nice big empty field underneath I am making into a beautiful park square and placing the cafe. I'd hate for it to be against a cliff wall or tucked into a corner. I have yet to see it beside the ocean though! That would be pretty.
I have mine in the centre, which is awesome, and my town hall is above it. I placed a fountain between the both of them though, which I thought was a great idea, but I'm worried that as the tree grows it will block the view of the fountain / town hall. I've seen pics of how big the tree gets, but I don't know if it would block these out or not.. so I'm all paranoid. D: