Hotels.com five-star program stands out in my experience as consistently and genuinely helpful. When you get mediocre service from so many other customer support departments, it's a pleasant surprise that five-star customer agents always go the extra distance.

They've helped me with the price-match guarantee, helped me resolve a non-refundable booking that was entirely my mistake, helped me book multiple, international destinations that weren't totally supported by their database, etc.

I don't know how five-star plus service differs from mere five-star. If there are any 5*+ members reading this, would love to hear your opinion of whether it's worth it.