The analysis is simple and has been done many times before, if you do a search you will find some good analyses.
First, you have to like the product and it has to be available where you travel. Only you can make that call. Personally, I don't do Starwood because I have had numerous bad experiences at their lower end properties (4 points). I am also not enamored with Hampton Inns - if you visit the Hilton forum you will see they run a thread with good and bad Hamptons. The Marriott product is very consistent and their properties are almost everywhere. (Hilton Garden Inn is great but there aren't very many of them yet).
Second, you need to look at what you get for a stay. The fairest way to do this is to look at what you get in stay value ($) for a given spend. So for Marriott, say I stay 75 nights in 30 separate stays at an average room rate of $150 a night. My spend would be $11,250 and I would get 112,500 base points + 30% Platinum bonus plus 30x500 in Platinum arrival gifts = 161,250 points. This does not include any bonus promotions which are frequent and generous. For 130,000 points I can (and have booked) a week at the Vail Marriott (Category 6) in peak ski season which runs $400 a night. So the points are worth 2.15 cents each if redeemed this way (admit this is a pretty good and lucky redemption - I usually value my points at 1.0 to 1.6 cents each).
So for a $11,250 spend I get $2580 in value (using the more conservative 1.6 cents per point), $2580/$11250= 23% return on spend. Do the same analysis for Starwood and Hilton and adjust for your spend and status, as well as your redemption patterns. But remember, first and foremost you have to like the product and it has to be available where you want to go (both for earning and burning). On the latter point, we like to go to Hawaii. Marriott has 10 properties on Oahu, Maui, Kauai, and the Big Island. Hilton has two. A week at the Marriott Lihue or the Marriott Waikoloa is 130K points - the Hilton Waikoloa is 175K and you have to walk to the Marriott's beach (Anaeho'omalu Bay). We just got back from the two Marriotts I mentioned above, at the Luau on th Big Island was a couple from Texas who were staying at the HWV. They asked what islands we liked and we said Maui and Kaua'i were our favorites. Long face from Texas man, and he said, "But Hilton doesn't have properties on Maui and Kaua'i."