For my preference, yes the rui was the best bargain, as they were close to the s8f, but for significantly less money. The s8f was better, but not by alot, so while an upgrade, is it worth the 200.00+ for the buyer? Maybe, maybe not, depending on how ones budget is an what they're looking to spend.
I would also take the s8pro over the s8f, but that's only because they are unique to my collection, as I already have an iem that's similar to the s8f, but I have none that is like the s8pro.
I would ultimately recommend a particular fearless product depending on ones budget and sound preference.
So, if you're wanting a fun and energetic sound signature and want the best bang for buck in the fearless lineup, then I would recommend the s6rui. If you're a musician or favor true stage accuracy, than I'd highly recommend the s8pro. If you want the best fun and energetic sound fearless offers, than I'd recommend the s8f. If you're a mids head and value vocals above all else, than the s10 genie is my rec.
*disclaimer-
I have not heard the Paladin lineup, nor the hyper s12, so my opinions are based on the Start-acme8.