Suppose my criteria would be :
Low powered - smoother and will not damage my pellet catcher too much, I wrecked the "niceness" of my Original 35 by pushing it to the limit and regretted it.
Well made - so older stuff or target stuff. also easy to work on and get to know.
Inexpensive - so you can start a collection as one is never going to be enough once you start! And so you will not wince too much as you saw 2" or more off the butt to get it to fit you better

Best cheers
George