I am currently using a PVC ball valve on my sniper, it wasnt the best move i thought at first, But to be honest i dont really regret it.
I find it the most reliable, Alot of the other types i have used let out the air to slow or in limited amounts, With just a really basic ball valve i can hold quite alot of pressure and get all the air out quick
The type of valve i am using (I was buying parts at bunnings and saw this, i was like what the heck ill just use this instead of thinking of a trigger mechanism)

really supprised how such a simple valve works so well!