Size would be the biggest difference.

QF = 7 feet or more in height

FL = 6 feet maximum

MF = 4 feet maximum

Besides that, there is not a tremendous difference in the bloom stature and colors, and there may be a slight variance in exact bloom times (all should be within a month of one another; June, July).

thanks for your reply. I bought the magic fire in May and it is budding right now. I like the idea of compact size since I don't have much space in the backyard. I was mainly concerned about the bloom quality among different "Fire" Hydrangea. I was planning to get the FL next year. I guess i will stick with the "Magic Fire"

Looks like Firelight might have slightly denser bloom clusters than the other two, which are a bit more open and lacy looking than most H. paniculatas. Quickfire is the earliest of my H. paniculatas, and will open here in central NH in the next week or so, but I don't have MF or FL.

Agreed with Babs on FL bloom type. FL should probably be easier to obtain over the long run, since it's a Proven Winners entry, which are sold at all major big box retailers, as well as independent nurseries.