Either ball or gate will work fine. Yes gate can allow more control, ball's are typically cheaper. It's a personal preference thing really.
Never heard anyone claiming that valving the output ruined their seals before. That is very interesting. I could potentially see too much backpressure doing that long term, but it's really not that different as Ach1Ll3sH33L mentioned from adding inline components or having additional head height on your return run. Mechanical work is mechanical work.