Difference between Astelin (azelastine) w/ Flonase and Dymista? Is Dymista stronger?

Same. While I love Dymista because it combines both a steroid and an antihistamine sometimes it can be very expensive. In situations where affordability is an issue, I often prescribe the components separately (azelastine and fluticasone) in order to save patients money. Both are equally effective, Dymista's advantage is that its all combined in one spray.