We too own DVC and Marriott and although it's great to have both I would suggest you buy DVC if you are buying to go to WDW every year or every other year. Orlando timeshares in general are not considered a great buy because there are so many of them, and certainly many Orlando timeshares out there are much cheaper than Marriott.
As you grow older your needs change and DVC is so flexible your reservations can change with your needs. With Marriott, as has been pointed out, you are pretty much locked into a) a week or season, b) a full week's vacation at a time, and c) a unit size. You really need to go to a Marriott presentation somewhere to find out all the advantages of owning a Marriott. Marriott presentations are usually very low key and not the hard sell you get at most timeshares. Both Marriott and DVC have 1st class accomodations and I highly recommend both of them, but as I said earlier, if you are buying to go to WDW, buy DVC.
As you grow older your needs change and DVC is so flexible your reservations can change with your needs. With Marriott, as has been pointed out, you are pretty much locked into a) a week or season, b) a full week's vacation at a time, and c) a unit size. You really need to go to a Marriott presentation somewhere to find out all the advantages of owning a Marriott. Marriott presentations are usually very low key and not the hard sell you get at most timeshares. Both Marriott and DVC have 1st class accomodations and I highly recommend both of them, but as I said earlier, if you are buying to go to WDW, buy DVC.