I've been using Ctrip for ages, mainly because they've swallowed up so many competitors. The Trip.com rebranding is confusing (good sub-discussion point, though), so let's try to stick with calling it Ctrip when talking about China.

I tend to lean towards Ctrip for hotels because of their negotiating power with individual properties (and not just in China). When it comes to flights, while Google Flights is great, it doesn't always provide the most comprehensive information, and I've found Ctrip to be reliable, especially for domestic flights within China or departing from there.

One of the biggest advantages I've found with Ctrip is their customer service. Dealing with airlines directly can be challenging, especially when it comes to reaching them. With Ctrip, it's far easier to resolve issues or make changes to bookings. Some may argue that adding a middleman is always bad, but my experience has been that it's okay if it results in greater efficiency overall.

I think it's worth having a focused discussion since many of us use it often, despite my general resistance to promoting specific companies in industries I wish were more competitive. I trust that 90% of you guys understand the "GBU" reference.

ETA: The reason I finally created this thread today, as opposed to 15 years ago, is because I've been talking with them a lot (i.e. 5x/day) since May 1, so I have an improved understanding of how things work. But, I'm not including these accounts in the OP because I want to keep it generic.

Edit #2: Here are the current China customer service phone numbers I have for them. 95010 and 400 830 6666..and 021 6066 8691 (English).

Edit #3 Here is a link to the other ctrip thread that was started at around the same time as this one:
How reliable is Trip.com?