I'm active with both programs. From an upgrade perspective, I find them similar: Gold gets you a good room, but generally not a true suite in a full-service property. However, because Hilton has OLCI at most of the props I've been to in the past year, I feel like I have more control over my upgrades. It puts my mind at ease to be able to view 3-4 different upgraded options and pick the one I want.

Also, Hilton lounges tend to be open more than Marriotts. And if you find yourself at an HH without a lounge or with one that isn't open, there's no question about breakfast: they will give you vouchers for whatever the next-best option is. At Marriott, you sometimes get it, sometimes get it after groveling for it, and sometimes don't get it.

In short, HH treats its Golds a bit better than Marriott, even though HH Gold is far easier to attain the MR Gold. I find it especially true in "resort" style properties.

Now for the flip side: there aren't many bad full-service Marriotts/Renaissances in the system. There are unfortunately a few more duds in the Hilton/Doubletree system. The best argument for Marriott loyalty is that if you travel to many cities and frequently book hotels blind (that is, no time for detailed research), Marriott/Renaissance generally won't do you wrong.

My opinions differ at the lower brands - I think HH wins on some, MR wins on some. But for full-service, the consistentcy of Marriott is higher than that of Hilton IMHO.