Priceline - Thieves + Worst Customer Service Ever.
Travel and Hotels
1. I did a road trip in the US in 2012 which involved several hotel reservations that I unfortunately chose to do with Priceline. Three of those reservations were charged twice each on my credit card. Once by Priceline and once again by the hotel. After several calls and emails I was able to get refunds for only two of these reservations and I can't get a refund for the third one until now.
2. I booked an airline ticket in October 2012 through Priceline and I had to cancel it. They cancelled it and told me I had to use it before September 2013. I now needed to travel in August 2013 and return September 6, 2013. They refused and had me call the airline 3 times with no hope of being able to get it. Finally I decided to book a one way ticket and even when the new ticket was cheaper than the one I cancelled, I didn't get refund from them for the change of price.
In summary, keep away from Priceline even if it costs you a little more. It'll save you a lot of headache and money if anything went wrong.