2.5mm² is the most common size and should work with a vast majority of speakers out there. Most likely the speakers it won't work with are ultra-cheap low end speakers.
The Van Damme Studio Blue is very popular and pretty reasonably priced.
But Van Damme Blue is pretty thick because it is Double Insulated. Take a close look at photos of the wire. That's perfectly fine for front speakers, but it might be a bit thick to run to distant rear/side speakers. Nothing wrong with that, I'm just asking you to keep it in mind.
For rear or distant speaker, again depending on your specific situation, consider QED 79 Strand (2.5mm²) which is single insulated so not quite as bulky.
Again, no problem with running Van Damme Blue to rear speakers. I'm just asking you consider whether the size will be a problem for you.
Steve/bluewizard