If your definition of 'better' is 'cheaper', then yes, it is better to get them from an authorized reseller. The caveat being that if you are booking something that requires a package, then buying the tickets from a non-Disney source is not better.
You can save a good chunk of change if you buy from an authorized dealer like undercovertourist, visitorlando or theofficialticketcenter. These all have discounted tickets and have good reputations for being one of the best places for discounted THEME PARK and attractions tickets.