Ashley,
It all depends 🙂
Marketo is great for PPC landing pages because you have the ability to quickly spool up new pages for your campaigns. But, if your website pages are optimized for conversion and you can make changes to them quickly, then that's good as well, and you can get the most "bang for your buck" that way. Most companies' pages aren't optimized for PPC, so that's why they use Marketo pages.