I've used WWTMS perhaps a dozen times and never had a problem. I even had to cancel and re-arrange my booking a couple of times. Again, no problem. I find the prices competitive.

I've also used expedia and travelocity quite a few times. These occasions have usually proved error free but I did run into problems once in Dijon where my hotel insisted my bill had not been pre-paid and they wouldn't let me leave without paying. In fairness I did get re-imbursed by the travel company who also apologised profusely (I think it was travelocity).