It depends on what your doing. I like Hydraclean from Hydramaster, it is an alkaline extraction solution. If however I am cleaning a carpet and want to leave it neutral after using a higher ph prespray, I will use Clearwater rinse from hydramaster which is an acidic extraction solution. They are both useful in different situations.
Some acidic rinse agents have no more cleaning power than water, all they do is neutralize the prespray. There are others which do like Clearwater rinse, Optimal rinse and Fiber and Fabric rinse.
There is also a neutral extraction chemical from a company called Craftex which works surprisingly well.