I will give my opinion:

Marriott:
+
Travel packages ^ ^
LOUNGES ^^
BREAKFAST at all FS/Ren m-f ^ but not weekend
Megabonus ^^
-
inability to book suites on points
no bfast on weekends
no bfast at resorts

Hyatt:
+
book suites on points ^^
bfast 7 days a week ^^
modern deco ^
-
Hyatt place
not many of them in the US/Europe

Hilton:
+
still struggling on this one
-
in my opinion, DATED properties
Lounges stink
bfast coupon routinely NOT for full bfast
did i say DATED properties?


To sum it up for me-
Marriott is great for a week long stay using travel package, although I am migrating some business to Hyatt due to 1-bfast 7 days a week (worth a few HUNDRED for my wife, son, and I on vacation), and 2-ability to book SUITES with points. This is HUGE to me. Marriott puts 5K points/night for a suite, but I have NEVER been able to use them!