don't overlook the ability to mix and match them, because each "axis" is good at its own things

  response.xpath("//div[string-contains(@data-foo, "foo")").css(".some-class").re(r"[a-z][a-zA-Z]+")

The .css() flavor gets complied down into .xpath() but there is no contest about their expressivity: https://github.com/scrapy/parsel/blob/v1.9.1/parsel/csstrans...