While Hyatt offers many great benefits, upgrade is not one of them.

Although SPG has become very stingy lately with upgrades, over the course of being Platinum with them, 95% of the properties do upgrade Platinums to their best available room, including suites. I've had about 30-40 stays at Hyatt so far, and only 2 properties routinely upgrade me to their suites. All the other ones, including Park Hyatts, usually put me in the lowest category room. When upgraded, it's usually only one category.

Now, you may argue, that Diamonds get 4 confirmed upgrades per year, but the T&C prohibits those to be used with any promotional offer. Recently, I was denied the usage of a suite upgrade when booking ANDAZ5 at an Andaz . The definition of "promotion offer" is vague and properties do use this to their advantage in denying upgrades.

So, the bottom line is, what do you want? If you want tons of free nights and points, free breakfast, excellent private line but no upgrade, then stay with Hyatt. If you want overall better upgrades, the ability to stretch your award with cash and point, and better and more properties around the world, then go with SPG.