I just looked at a few hotels on Marriott and compared them to hotels.com and found the Marriott price generally cheaper, particularly with AARP or senior rate which cannot be used on hotels.com. But what happened to the Marriott web site? It used to be easy to use, now it is a fiasco.
For my personal bookings I almost always use the Hotels.com/venture link. I was recently at a Hampton which was full and the desk clerk told me that I had the cheapest rate in the hotel that night (I had rebooked I a couple of times when it went on sale). Then she asked me why I hadn’t booked direct. I always check the hotels own web site when I book and very rarely is it cheaper when the free room and the credit card fee are taken into account. I am only booking perhaps 20 rooms per year. If I was booking 100 a year like the OP I believe it would drive me to stick with one chain because of the extra points that go with the status, and the other benefits.