a lot of people say prone is best, ok it cuts out a few 'variables' but, if you only shoot prone you'll never find you body posture for shooting standing.
basically with springers each posision is a case of sussing your 'still', its a line up on the target, when you find it it doesnt matter what posision your in. pcps i find a lot easier in all the positions.
(if your off posture your sort of squew wffed as you look at the target, as you squeze the trigger you get awful grouping or miss all together. even prone has a posision, it just seems easier because your not holding the gun in the