They're geared towards different goals. LC is for interviews: solving small scale problems of the scale you might get asked in an interview or come up against every day in a software job. PE is more of about curiosity and personal intellectual development. It asks something that you might never have heard about and might never see again but is often very interesting, and will stretch your ability to develop your own algorithms or to apply learnt methods to unfamiliar scenarios.

I'd recommend LC to someone who has an interview in a month, PE to someone who has one in a year.