I've not been to Cabo, been to PV several times and was married there so I'm biased. People who came to my wedding that had previously been to Cabo were surprised by PV and preferred it for it's romantic and authentic Mexico feel, but maybe that's just my crowd.
Cabo is desert meets ocean, PV is jungle meets ocean. From what I've seen/heard/read about Cabo it seems to be more commercialized and upscale, whereas PV seems more quaint and rustic (although I'm sure both places have the cheap and expensive spots). You can be the judge from all the pics/reviews here and elsewhere on the net. Good luck!