stevekoe,
I am a Diamond member with Hyatt for 2 years and Hilton Diamond for just under a year and Marriott rewards silver for 3 years and here are my feedback.
As a diamond, Hyatt really looks after you. YOu get an amenity, typically beverage (red wine, white wine, beer, soda sometimes Cava/sparkling wine) and and snack (cheese, fruit, nuts, etc.) which may vary property by property. The most memberable two are at the Park Hyatt Toronto where access to the changing room (cost $20) and heavenly doubledipped chocolate strawberry at Grand Cypress in Orlando. Both were award stays and it did not make a difference to my amenities.
You also typically get continental breakfast or other breakfast as a Hyatt Diamond. I know in the Grand Hyatt near Central Station, they accepted my diamond breakfast coupon for their buffet on the weekend and it was a decent spread with smoked salmon.
For Dallas, I would not recommend the DFW Hyatt. Was there late Oct after a conference but before an early flight on Sat. and it was not that great. Paid $100 and did get my amenities and breakfast but the place was in renovation and the rooms are tired. The only thing that was good from this stay was half of a FFN Faster Free night where for every 2 stays get 1 free night anywhere with limited/no blackouts.
My experience as a Hilton Diamond is limited to 2 property, one Hampton Inn in Miami which is fairly comfortable but no real special treatment and Hilton in Cleveland Beachwood where Gold / Diamond have access to the conceirge lounge. One thing I do not like is that if I do not make my hotel reservation until the day of arrival (when I forget), I do not get my amenities and the ameniites are hit and miss - changing from 1 beer and snack mix, hot chocolate in mug with some cookies, half bottle of wine and cheese, nut mix.
Marriott does not do much for their lower level elite althought some colleagues that are Platinum got a good reward skiing in Salt Lake with lift tickets for a few days.
Cannot comment on *W since I have only stay in them 2ce in the last 3 years but some of the Ws and Westins are nice.
Have fun :-)