Thanks to those who have answered seriously.
Gino, boxerbay, rjssigns this is not an Apple vs PC or which colour is the "best" type question. Obviously external weather conditions vary, print materials vary etc etc But I'm talking about "on average", "all things being equal", except for the ink / printer used. I would have thought that was obvious.
As you can see from the replies from people who bothered to add something of value, the general consensus is the Mimaki SS21 ink, in most conditions, is probably one of the most durable OEM inks around and this is bettered by the Triangle equivalent. No this isn't a completely exhaustive, scientifically definitive answer, but it gives us a pretty good indication.