The generics all contain the same ingredients, as do all chocolate chip cookies. Doesn't mean they're exactly the same. The new orange U30s are considerably stronger than previous types. I found the U30s to be much more stimulating than the cor or the barr brands, kept me up all night. Using 30-60mg of barr brand I can sleep within a few hours, but that dosage on the U30s had me tweaking for a full night with no sleep.
This can be good or bad, depending on what you're going for. I really enjoy the U30s. They seem quite a lot better than the pink Cors.
If I had the option, i'd always go with name brand Adderall XR for maximum effects across the board. Then I'd go with the U30s, then barr, and last but not least I'd take the cors in a pinch. Cors are better than nothing but I can take 90mg of them in a day and get nowhere near as high as a single XR30mg.
If it's all the same ingredients, explain that. To me, they all have unique effects.