Playing bass for more than 30 years, mainly 6 strings fretless basses, I've tried almost every strings available on the market, including exposed core and taper core ones, and always came back to the D'Addario XL Nickel Round Wound (EXL170 4 to 6 in my case). I also was a great fan of the Flex Steels, but they disappeared. I've now restrung all my basses with these EXL170 (4 to 6) and must admit it's the best tone I can get.
I was about to put NYXL32130 on my main fretless bass (Leduc Masterpiece MP 628 SF), but was not sure I had to do it because I really love the EXL170-6 tone and feel. But the NYXL32130 will be perfect for my Leduc PAD 6 (all padauk 6 strings fretted bass) as they will highlight the ultra fast response and punch of that wood.
Can't wait to try them.