It's interesting, from my comparisons lower loss solutions appeared to sound better. Losses are lower with increased wavelength, 1550nm is lower loss then 1310nm, 850nm, 550nm etc. OS2 fiber quality is typically lower loss, I have a slight preference for the ACT RL1700 series (RL1701 is 1 meter, RL 1702 is 2 meter etc). This is UPC (straight cut), I have an APC (angled cut) cable but did not prefer it, though it's an old used one I borrowed. APC does make sense though. I did not try attenuators, in fact I initially bought the Startech 80km SFPs as they are about the only ones I could find not requiring attenuation by factory specification, so it seemed to be counter productive. Will definitely try now though.
Here's a nice link to explain the differences between UPC/APC:
https://www.ppc-online.com/blog/picking-the-right-fiber-connector-pc-upc-or-apc