To go into more detail, really -- if you have a typical time of travel (F&W, marathon, spring break, whatever) there are generally 2-3 Use Years that might fit your travel style. If you travel all over the calendar, any UY may work for you. So, buying resale first, you have more options to consider.
If you buy direct first, beyond having to buy more points direct to get a master contract, you then make it so that you ideally need a resale contract with the same UY. So instead of being able to consider multiple, you limit choice.
Direct can always match your resale UY. Resale, you may have market issues matching direct UY.