"Best" is a strange qualifier.
Afinia premium brand ABS is the "*best*" I've ever used. Super smooth, super high tolerance, great color and appearance, etc. But it runs something like $56 for 700g, which is very expensive for me. It also prints at 260 celsius, which is hot unless you have an E3D.
Octave, Sainsmart, and Zentoolworks are probably our favorites on the forum here, because they're cheap and available on amazon with free shipping, hah.
But with Octave I've had filament problems before, same with Zentoolworks [only purchased one sainsmart though.] I've also had good rolls from each of them.
Monoprice is another place with cheap filament.
But its hard to call these places "best" though they're most affordable.
I'm looking forward to sourcing more of my filament from my filastruder, so I can get cheap+reliable, since I really dislike the unreliability of the cheap brands but cant afford the expensive brands.
Once I purchased 10lbs (min order) for $100 from Acme Toolworks, a plastic supply company, and it was actually super. *is* I still have a half pound or so left, haha. But that has its own downsides (a 10lbs spool.)
Inventables.com has a pretty good filament too, actually, probably my favorite in terms of quality vs price (a little pricier, but better quality it seems than the cheapo brands. *Qualifier* I have only purchased one roll from them, they could have bad rolls too.)
