i'm currently pregnant and my breasts have grown to the point where i needed new sports bras and re-measured myself. i'm between a 32 and 34 band (32.25 inch underbust measurement) currently, so this band fits on the tightest setting, which is fine for me because my rib cage is still expanding. if i were not pregnant, i would probably go for 32FF. but if you're in between sizes, i'd personally go with the larger band size because this bra does not have a lot of stretch. i think most of the support comes from the cups fitting properly.
as for the cups, i was pleasantly surprised by how supportive they are, given how lightweight the material is! the cup material is not stretchy; it supports in an encapsulation style (similar to wired sports bras, but without the wires) so you need to make sure you get the right fit. personally i prefer this type of style, and this bra in particular works wonderfully for me and gives good motion control even when running. that's right, no bounce!
the only negative for me is the straps. i'm 5'4" but have a very short torso and high-set breasts, so the straps slip on me and are a little too long even when adjusted to the shortest setting. however, the bra has a J-Hook to convert to racerback straps, so i use this and the straps fit fine. the only downside to that is that because the fabric is not very stretchy, hooking the j-hook causes the seam between the back closure and the straps to gap/wrinkle up. you can sort of see it even in the product image, but it's much more pronounced on me and makes it look lumpy under my shirt. i'm still keeping it because it works for running, but it would be better if it had the option for shorter straps, or was a true racerback style.