At the moment, Stihl CF3 Pro .105.
I've used .095" Stihl X-line for years. Tried Black Diamond .095" and was not impressed.
I've been buying short rolls recently to try various string out.
One day I went from .105 CF3 Pro to a coil of X-line, and immediately noticed more noise from the X-line. IE - less aerodynamic = more load on the engine.
The CF3 Pro also doesn't seem to weld in the spool. X-line and even Black Diamond seemed pretty bad about this. I haven't had a single weld with the CF3 Pro.
I think I'm going to stick with it for a while. So far, I really like it.