When you are living out of a briefcase, you can gain diamond or platinum status by staying frequently in Hilton or Marriott.
To me the two most important things that I look for in a hotel are internet access and courteous staff. I find Hilton to be better in both these aspects. Also, on an average, I can say that Hilton's Hampton Inn is better than Marriott's Residence Inn and Courtyard. I also like to stay in Hilton's Embassy Suites. I am not very fond to Hilton's Doubletree though.
Here is an interesting incident that happened on 06/02/2009 in Round Rock, TX. I had booked Marriott North Austin. When I went there I realized that they charge $10 per day for internet and $25 per day for the executive lounge access. I was already paying $145 per night for the room and the total came to $180. I called up nearby Hampton Inn and they had a room for me. They had free internet and friendly staff. I could now cancel my Marriott reservation (even though Marriott was our corporate partner) and move to Hampton Inn. I am glad that it was a wise decision.
In this case Diamond has won!