I’m the sole vote for spy/scout, but being a gunner is a close second. Does the lack of votes just reflect what you testers know about their current implementation? Maybe there is actual interest?
They are pretty bad. Movement is slow and not intuitive at all. It would be a bit better with a mouse but even then the lagginess of the controls and the inability to catch up to a fast moving target makes them almost useless. Also armoring them is almost impossible so even light weapons fire from AC or lasers quickly rips them to shreds as you are a sitting duck on the side of a ship. They are only effective when you have MANY turrets firing heavy weapons fire at a single ship and then some of the shots may get lucky. They came out with "dev turrets" that improved things slightly but it is still pretty bad.
Think of it this way...
You can have a HUGE expensive ship with 5 turrets (that you will probably not be able to fill all the gunners chairs). Each gunner can be taken out with a bit of weapons fire concentrated at any one of them. Each gunner will have a rough time landing shots on fast moving light and medium fighter ships that are possibly each carrying almost as much fire power as the entire large combat ship (this is not hyperbole, some fighters carry 10+ autocannons or other wapons). For the price of that single large combat ship you could instead have 5 or more light to medium fighters.
Large Heavy combat ships while being a lot of fun, are unfortunately not currently practical. Which is sad, because they are a lot of fun. Most of the problem lies with turrets, maybe tripods will fix them.