This thread should be labeled "my favorite
blowback", not "the best blowback".
The "best" is open to interpretation: best built? Most efficient? Most reliable? Lightest? Widest selection of aftermarket support?
The VM-68 was probably one of the most durable ever made. But it was also extremely heavy, had an oddball front-mount tank and was horribly inefficient.
The Spyder was light, efficient, fast, and brought a decent, mass-produced marker to a much wider audience. It was also unreliable, tended to chop paint thanks to it's cookie-cutter bolt face, and generally required cutting or replacing springs to properly chrony.
The Stingray was the first sub-$200 semiauto, and one of the first to be mass-marketed through the big box stores. It was also reasonably reliable, easy to fix, and lightweight. It was also cheap plastic, had no way to mount a bottomline or vertical expansion chamber, and had a horrible stock barrel.
The Alley Cat/Thunder Cat was very well made, had excellent adjustability, and was very compact. It was also a pain to dismantle for cleaning, could be touchy about velocity/recock settings, and took a never-used-anywhere-else oddball barrel thread which limited your options to the stock barrel or perhaps a Freak back- if you could find one.
The Illustrators were well made, quite reliable, light and fast. They were also difficult to clean (you needed a special tool to remove the bolt) had no vertical ASA option, and occasionally the glued-in feed necks would fall out.
Pro-Ams and Pro-Lites were extremely durable, very reliable, and at least adequately gas-efficient. But they were also fairly heavy (Pro-Ams especially) and somewhat bulky, again limited to back-bottle only, and had a trigger pull of an Arrow staplegun- worse, because of the air line, a 2-finger trigger wasn't possible.
Carbines were lighter, faster, more gas-efficient and just as reliable. But early models had wear-prone O-rings on the valve and not much improvement on the trigger pull.
The Golden Eagle was reliable as an anvil, but was roughly eight and a half feet long, got six shots per 20-ounce, and weighed as much as a small car.
Objectively, the "best" would likely have to be the Model 98. It's not unacceptably heavy, fairly air efficient, extremely reliable, and has a huge array of aftermarket accessories available. It's also been around for over 14 years with minimal updating, the trigger pull is acceptable, the velocity adjuster has plenty of range (generally speaking) and it has a nice, beefy barrel thread that both removes quickly and is virtually impossible to strip out.
But even still, it's fairly bulky, the mandatory front grip is kind of goofy, and it's difficult to open up for cleaning.
My personal fave? Probably the Carbine. Probably because I have three, and I used to trick 'em out a lot.