Didn't love GnR at first but it grew on me big time, been having a blast with it lately after fine tuning the flipper angles and powers. JP2 is one of the best, though. Depends on opportunity, I guess.
edit: So you have both and are trying to decide which to sell? Sell JP2 then. It hasn't been on the line for a while so there's demand + higher prices right now, but it will be run again in the future, probably a couple times at least. GnR's demand has cooled off now that they're pretty widely available.