Re: Hen or Rooster?
Either will work, if you select suitable feathers, and match them to fit the size & style of streamer.
I've primarily used rooster, and as Ard has said, have used Indian necks for some streamers. I use both strung saddles & strung neck hackle most often since I don't tie a lot of small sizes.
Really depends on the particular feathers. I've tied Matuka style streamers with hen since the more rounded feather tips are desirable for that style. But, some hen necks I've had the stems were too flimsy to tie suitable streamer wings, as they'll foul too easily.
Nothing wrong with using either if you have them.
Remember, no one likes to be behind the big truck, but that's better than being under it!