Marriott is much more flexible and less expensive to use than Disney. If you only want to go to Disney World, then it might make sense to buy Disney points.
For Marriott, buy a resale platinum week, a place you would like to go sometimes and wouldn't break the bank to exchange it elsewhere. In other words, don't buy Marriott's Ko Olina and use it to exchange. Hawaii fees are too high to use for exchange purposes. Almost every exchange is a downgrade in value.
There are some great traders out there, and some of the weeks are cheap on Redweek and TUG classifieds. I am considering a new one for trading purposes and see people giving them away. It looks like a no-brainer, maintenance fees are a bit on the high side because of the location, and trading power is high most of the year. But I can lock it off and get two deposits.
We own Shadow Ridge in Palm Desert, and it trades pretty well. Always buy platinum weeks.
Abound points cost a lot of $$ to acquire enough points resale to use for most locations. Weeks are just better.