What Should Authors Look for in a Book Publishing Service?

I’ve been thinking about publishing my manuscript and started researching different options online. There seem to be many platforms and companies offering a book publishing service, but it’s a bit confusing to know which one is actually reliable and helpful for new authors. Some focus on editing, others on marketing or distribution. For those who have already published a book, what factors helped you choose the right approach for book publishing? Any suggestions or experiences would really help.