GSX-R shock is best bang-for-buck value. Can get 4-way adjustability for less than $50. Look for posts on here where I show how to mount one without needing to hack up frame and shock.
I made comparison of various factory and aftermarket shocks here:
https://www.ninjette.org/forums/showthread.php?t=337292 . After trying both Ohlins and K-Tech Razr-R, I prefer the K-tech. Direct drop-in installation, easier adjustment and better performance.