Just got my third earlier today, it seems to have the lowest drop rate of all of them, which is only fair seeing as its the UR card. However in previous events that didn't seem to matter and only the URs were dropping for me and I had to farm just for the SRs
That's the wacky part, sometimes UR just keeps dropping while the SRs are nowhere to be found, when logically it's supposed to be the other way around.