In honesty, it's the standard.
There's virtually no other rear damper on any decent production bike that uses this level/spec of shock.
That being said, I have a RockShox Monarch 4.3 on one bike (I have the RP23 on another) which is actually very good - underrated, I reckon.
The side benefit is you can buy a Monarch (there's several models) from overseas for much less than you can buy an RP23 locally (Fox won't let you buy from overseas, they don't allow their retailers to sell offshore).
Worth a look if you're in the market.