i'm not sure how reliable each of the markers are. I would go for the piranha for reliabality and the spyder for features.
the piranha and the spyder will be able to operate at lower pressures than older versions.
For the spyder you will have to buy an elbow to fit on the shutter.
You can choose between a vert feed and a power feed for the sts before you buy.
On the vert feed piranha you won't need an elbow (on vert feed spyders you need to buy an elbow)
Thats all i can think of right now.