This is really scary. I was just about the do a similar poll.
Here is my idea of it:
Here is my choice and reason.
Bumper cam: This is the cam I always fall back to. I was only able to get the GTone challenge done using this cam. So I owe this cam a lot.
Cockpit cam: Initially I did not like this cam because it makes the world outside smaller. So everything looks smaller and with less detail. On the other hand I must complement PD on the way they implemented it. You have the feeling of sitting in the drivers seat. Still I thing this view is not suitable for long periods of racing, because it strains the eyes.
Roof cam: Initially this view was introduced with GT4. I always thought PD was trying to do a bonnet cam. But apparently not, as with some cars this view is just plain awful. Especially the Le Mans cars are great with this view.
Good point about the view is that you see the upcoming road very good.
Bad thing is that when you have car that has weaker springs, you end up getting sea sick during cornering.
Chase cam: Love-hate relation with this. Love to look a the $exy cars. Hate it because of the lack of control when during serious racing. Anyone managed to get the GTone challenge right with this view?
So I revert to the bumper cam most of the time.
While using the cockpit cam I noticed that the Nissan Skyline pace car has a transparent banner that show the Gran Turismo text and logo in mirrored. It's a shame other cars do not have that, while you can see such banner from the outside view.