I have all three. They all have the same failing - no calendar. You have to know the dates and days of the week ahead of time. For instance, if you want to go the second weekend in May you can't look at a calendar and see when it is. You have to know them and then input the dates.
My personal favorite is D-Point. It is not the "slickest" but it gets the job done, and then lets you change key items like resort, dates, room type, etc. easily and gives an instant point tally.
DVC planner lets you save your trips and gives you advance warning of the dates you need to call, i.e. the 11 month, 7 month, etc. But it is a bit clunkier in the way it computes the points, and it is not as easy to change a single parameter and get a new point value.
DVC points is very similar to D-Point in terms of function. The main difference is you input a start and end date, with D-Point you enter a start date and number of days. Otherwise they are about the same.
It just depends on what you want to know. Just how many points for a stay? Then D-Point or DVC points. Need to know the advance dates to call, want to save the trip? Then DVC Planner is for you.
Of course, for under $3 you can have all three! As soon as one offers a calendar then you'll have a winner. Otherwise there is not enough difference to really pick a winner.
Good luck!