When I first started travelling, I bounced around between a few different hotel brands before settling with Marriott. I was travelling around North America.
I found that Marriott had the best mix of locations and cost. I would generally have a cap on the amount I could spend, and Marriott generally fit under the cap. I liked Westin, but Westin was generally more expensive, and I don't find Sheraton as nice. Hyatts weren't around enough. Hilton was decent, but I found the Marriott hotels tended to be more consistent in quality.
Now that I live in the UK, Marriott isn't as convenient due to lack of properties, but hopefully that will change Marriott increases their presence in Europe.
Greg