Marriott and DVC are 2 different animals. They each have their benefits and negatives. There are a number of us that own DVC and other timeshares including Marriott's. I personally own 3 DVC contracts and 3 Marriott weeks. What's best for one is not the same for another.
Marriott is more of a traditional timeshare where if you want to try a different Marriott resort, you must exchange there through Interval International. In general you get a full week for either a fixed week and unit or a floating unit/week during a specified time frame. For someone who wants to try the different DVC resorts, stay different units sizes and different lenght's of stays and travel different times of the year; DVC is much better. If one can stay for a full week, generally needs a 2 BR, can predict when they want to travel and wants to do other timeshare trading; Marriott is a better choice.
The HH off season deals are actually available to most II members, not just Marriott members. Manor Club is nice but it does not have good exchange power, just like Orlando. Maui Ocean Club 2 BR Ocean Front is very expensive but if you need a 2 BR, want to travel most years to HI and are willing to pay for it; that's the way to go. It's not worth it to me but it is to some. I've actually seen MC weeks for $8K for Platinum. The specific resort and season, even view type, has a far greater affect on value than with DVC so there is more variability.
As for resale value, it depends on how you look at it. DVC will hold it's value a little better than Marriott but the issues are the same. I bought a second Marriott Grande Ocean week last year. I paid about 60% of what Marriott resale office charges which was about the same price the seller paid new. I did not get the points options since it was resale not through Marriott and could care less. I could however sell my two GO weeks for a larger profit than my DVC contracts.
As Shontell said, I think DVC and Marriott complement each other nicely. Marriott has more resorts, more areas and in some areas nicer resorts, HH for example. It's also somewhat of a personal preference. Believe it or not there are many out there that would prefer to stay off WDW property and therefore prefer Marriott's in Orlando to DVC.