Many hotels are now indeed offering member rates which are usually the cheapest.

Some 3rd party sites do occasionally give you cheaper rates (see the Expedia case above). If you decide to go through a 3rd party, you have to make sure you compare a few things vs the hotel's own site:

--the final price with all taxes and fees included;

--the room type, bedding arrangement and potentially, meals included

--the cancellation policy

Sites like Expedia, Booking.com and Hotels.com all offer various loyalty programs though. My colleague raves about the free nights he gets on Hotels.com. You just need to evaluate based on your own needs.