Say you were tasked with supplying an air rifle rental range with spring piston rifles in .177, .22, and .25 calibers. The rifles need to be durable, easy to maintain and repair, and be mid-range in power so they can knock over targets with authority.

What would you choose in each caliber?

RWS 34P for .177 and .22

First, very little maintenance is required for spring guns. Probably isn't going to be much of an issue.

In the event that it's necessary to tear into them, there really isn't much difference between guns like the RWS 34 and the Weihrauch HW95. A spring compressor, a couple of pins and you're good. I've heard rumors of frequent broken springs with recent production RWS 34s. The good news is that RWS guns carry a lifetime warranty. Box 'em up and send them to Umarex. The Weihrauch guns should run and run and run.

I have had a RWS 48 for over 20 years, 3 kids and 5 grandkids  have dinged dented  and generally abused it. I has never required anything more than cleaning and oiling ..

Beeman R series (HW) rifles. The R1 is King!

Have you ever owned or shot an R1?

Can't think of a .25 springer that I would say is "easy to maintain".   I've shot a few, currently only own one, but I wouldn't recommend that caliber in a springer.  Also, it's my experience that most .25 springers are tough to cock, which may be an issue for folks on a range.  In .177 or .22, even though the up front cost is high, I'm going to say the AA TX-200.   I've never owned a spring gun that was so easy to work on.  Hell, you don't need a compressor to pull the main spring.

Edited to correct spelling.

In .177 the Feinwerkbau 150 and 300 rifles are impossible to beat. Their pistons have a steel piston ring, much like in a combustion engine, that will last very, very long.

And do you have a muzzle energy level in mind? Does medium mean about 14 to 20 Ft*Lbs? What kinds of targets will you be using?

Are we on a shorter range, like 20 meters or less? Or, more like out past 40 meters?

The risk to the targets and ricochets and splatter are real. If you smack a small metal target with 20 Ft*Lbs at less than 10 meters, the targets will take a beating.

I'm going to take a loose guess and say that for metal swingers or knock-down targets at ranges of 10 meters or less, you may want to limit yourself to about 7 to 11 Ft*Lbs. If you are going out to 40 meters, then the medium power springers in the 14 to 20 Ft*Lbs class will do the trick, but the close targets could suffer and there is a back splash risk.