I use XMarks, too, but I haven't been syncing on a regular basis for several years now. Back in 2013, their extension would cause the browser to hangup from time to time while a sync was going on. Unfortunately, this affected a very small number of people, including myself. People who had many bookmarks. I tried it out again back in December and it works flawlessly now, but I haven't had any bookmark issues in the last few years. I like Chrome's ability to upload and download bookmarks tied to a Google account you sign into the browser's settings. That's very neat.
The only issue I have with XMarks is that you can only upload one set of bookmarks per account. If you have more than one browser and there's no unification of bookmarks on all of them by your choice, then you need to setup different accounts. That is a major pain in the butt.
Edit: According to my account history, the last time I uploaded my bookmarks was April of last year. And the first time I uploaded was in March of 2010. Which seems accurate. When I began using it was called XMarks and was referred to it by someone I knew on another website. And he had been using the service since the FoxMarks days, IIRC.
Edit 2: So what I thought was December was actually April of last year. Yeesh.