As stated before Munich Marriott and the Ren are basically next to each other. However the Ren is maybe one minute closer to the "U6" subway station "Nordfriedhof".

Ren usually upgrades Plat members into junior suites with a seperate living room whereas the Marriott usually puts me into into a standard room but adds a large fruit plate as an additional welcome gift. So if you are looking for a larger room the Ren is the choice. If looking for a modern bathroom and wellness area (steam room, sauna, pool, jacuzzi, state of the art work-out room) go for the Marriott. Breakfast buffet is nearly the same and will be granted to elites in both hotels. Marriott does have a "show kitchen" wheras you must order your omlets at the Ren.

The Courtyard Munich is a nice and very modern hotel. I have not much of upgrade experience as i was there only twice. IIRC got a larger standard room and the breakfast buffet comped. Location is in walking distance (5 minutes) to the main station and "Karlsplatz/Stachus" (=pedestrian area).