We're assuming you're talking resale. Disney has in the past basically only sold one resort at a time, or if having two different resorts, had different incentives to purchase at one resort over the other. Remember, once a resort sells out the only way to purchase there is via a resale, or from Disney wherein they got points back from a ROFR sale. All
DVC resorts are currently sold out except for Saratoga Springs and Animal Kingdom Villas.
As for being the cheapest, the annual dues can make a difference. For example, buying reslae, VB is usually the cheapest, but has the highest dues. Over time, the extra dues you pay will eventually pass up any savings you made on the original purchase.
Also, buying an offsite resort such as VB only gives you the 7-month booking window at the WDW resorts. That could be a problem for certain times of the year.
The best is to choose which resort you'd like to stay at the most, and purchase there. That gives you an 11-month booking window. Also, don't forget that the resorts have different end dates. Depending on your current age, that may be important.