The primary difference is face milling.  The Selects have a deeper mill while the Studio Selects have a smoother/cleaner mill if you will.  Deep milling makes the putter sound softer, and therefore makes the feel softer.  Some players doprefer the sound of the non-deep milled putters.  It's a little louder or crisper providing a little more feedback.  

It's noticeable difference in sound so I'd recommend finding a Showcase partner to test!  We happen to have one left.  It's a Newport though.  

Ryan brings up a great point, putters are personal and some people really like the deep milling while others prefer light or no milling...you need to hit both to determine which is your preference...

Good Luck!