A shackle flip will be much better than rc springs. Most people on here dont like rc because they are stiff. The ride will be much better with the shackle flip. A shackle flip will also offer a lot better flex than the rc springs. I dont know how much rc springs are, but I know most shackle flips go for under $200. As for longevity, with a shackle flip you are using your stock rear springs...so they are not new. However, I highly recommend going with the shackle flip for the fact that it will ride much better, flex much better, and rc springs are really stiff.
-Harrison
