I don’t fully understand how OP’s thread title matches up with what OP wrote in their post as it appears to discuss only Marriott and Hilton credit card earning.

Regardless, some interesting points have already been made in the responses, and I have some thoughts, as well, as I have been Marriott Ambassador, Hyatt Globalist, and Hilton (Credit Card) Diamond for at least 2 years (Ambassador and Globalist for more than that).

One thing - I generally like Marriott more than Hyatt - there are more hotels in more locations, and my Ambassador treatment has generally been the best of the bunch. I am also partial to some of Marriott’s brands - especially Westin and Luxury Collection. However, Hyatt does have some pros:

• In the US, in hotels without lounges, the breakfast offering is usually more consistent and covers tip charges. We all know that some Marriott properties like to place limits on breakfast in the US. With Hyatt properties without lounges (so every brand besides Regencies and Grands - and even then lounges in those brands aren’t universal), you should get a full hot breakfast covered 100 percent. This is not as much of an issue outside of the US as Marriott breakfast offerings outside of North America generally include a full hot breakfast.
• Also, in the US, Globalist gets no destination fees on paid stays - this can be really nice.
• The Category 4 certificate doesn’t necessarily have to be low-end. I have used mine at the Park Hyatt Jakarta, which is a fantastic property in Hyatt’s top brand.
• Hyatt has an award chart (for now)
• Milestone Rewards every 10 nights can add up
• I care less about this as I generally only do short stays and dislike having to call in to use them - but Hyatt’s SUAs are valid for up to 7 nights per award certificate and could theoretically confirm a suite months in advance

That being said, Hyatt’s footprint is rough. I personally would not want it to be my only program. If I had to pick one, it would be Marriott with Ambassador.

If OP could provide more details as to their travel patterns and what they are considering regarding Hyatt, that might help the discussion.