The difference between all 3 of the autoFlex models would be the target audience, as one model may result in better performance for certain players, whereas another model may result in better performance for other players. Ultimately, a premium golf shaft should feel good and right to the player's body.
Both of the newer generation(Dream and Joy) shafts carry the same concept as the Original (easy to swing and increase kick at impact), but the materials have been upgraded to the latest and greatest carbon prepreg material from Japan for both, which has allowed the shaft to feel even better. Their KHT (Korean Hidden Technology) is now in their 2nd generation. This is their special sauce, we don't know how, we just know it works.
We have posted the recommendation tables on each product-page for reference.
Original - The stiffest overall, has the original autoFlex feel.
Joy365 - Softer feel in the hands than the original and even more kick - designed for slower swinging players to help gain the most efficient height while being very easy on the hands (ex. ladies and seniors)
Dream7 - Slightly softer than the original but with an upgraded tip section for more stability and power at impact.