I like YYSL Type X and Regular Poly. Only in neon yellow, of course.
It sounds like toxics are the most used generally. I’m thinking I may order some pretty soon! 
I’ve never really paid attention to what string is set up on what yoyo. As I tend to make my strings last/push it to its limits, I tend to use the stock string that came with my yoyo. I have a pack of the 100% poly YYE strings as well which works nice. Otherwise, I twist my own strings and actually just got a spool of Kevlar-based string, about 2 miles worth. I just made my first string with it to put on my Littles (I make a custom, slightly thinner string for it) and it feels great!
I also have a spool of 100% poly thread that’s used for mattresses which works pretty good, have never snapped it but tends to fuzz up pretty quick. It’s more shiny and slick than your typical poly string.