DEPENDS ON THE ORGANISATION
To begin with, as others have stated, the titles are sometimes interchangeable depending on the company. For example, a PM position at Microsoft is equivalent to a PMM position at most other tech firms. I’ll assume that PM = product owner who has engineering resources and ultimate responsibility for shipping the product; PMM = responsible for “outbound” 3Cs (customer, company, competitor) and 4Ps (product, price, promotion) (product, price, promotion, place). In some companies, such as Amazon, the PM and PMM roles are combined.
WHEN IS IT IDEAL?
If you want to be close to the product, enjoy working with engineers, and enjoy developing things in general, PM is a good role for you. If, on the other hand, outbound marketing is your thing, PMM is the way to go. Experts would recommend that you speak with representatives from both of the companies (from which you have received offers) and present your concerns/questions.
Finally, every industry has a seat of power, and in technology, that seat belongs to the product team, which includes engineering, project management, and project management. It is possible to begin as a PMM and progress to PM over time. According to my discussions with several senior product managers, the closer you are to the product, the more power you have. In that sense, PM may be superior, but the decision should ultimately be driven by what you are passionate about.