Different people are going to value different things in a glue so may have different ideas about the best glue. Here is what I want:
1. Ease of use, which means even drying not to fast, not too slow, so you don't get clumping, and not too runny but not too thick either. I don't want to make a mess.
2. Don't want to have to use more than three coats -- one on blade and two on sponge. I don't particularly enjoy gluing rubber to blades, so would just as soon get it done as quickly as possible while still getting the best attachment.
3. Want even attachment that never starts to detach around perimeter of the blade, and rubber as flat as possible, idealy without any ripples on the surface. But the glue/rubber should never shrink either, at least not while the rubber is on the blade. I want the glue job to give me the same playing properties for the same kind of rubber to the same blade every single time. The glue should never be a factor affecting the play (which is why I don't seal blades).
4. I want it to detach without damaging the blade but I personally don't care if it comes off the rubber. I do not like to use sealants on blades. I use a hairspray trick that works fine, but isn't adequate to protect from super strong glues like Donic Blue Contact.
5. I want it to behave the same way every time, to be stable in a 100 ml bottle (so I can use the whole bottle), and to not have drying properties that are highly affected by ambient humidity.
For me Butterfly Free Chack 2 has all those properties (and far better than the original Free Chack) but maybe other glues do too. I haven't explored the entire market space.
Now, some people are going to look for other things for very good reasons.
Some people want their glue to easily come off the rubber because they are constantly putting the rubber on different blades and such.
Other people use blades with very fragile top plays.
Some people need to attach heavily boosted rubbers that are doming like crazy, and large-pored sponges like Tenergy and MX-P can be harder to attach.
Some people like messing with their blades and don't care how long a glue job takes (after all, it's their hobby!).
These things entail trade-offs. For example Rev 3 comes off the rubber completely and easily and will never damage your blade, but in order to get a consistent result (according to the video of the guy who produces the stuff), you need to put lots of coats on the sponge and several on the blade too. And even then, especially if you use a sealed blade, in my experience the rubber can sometimes begin to detach around the edges. All those coats add weight and the entire process takes quite awhile. After my first bottle of Rev 3, meticulously following the instructions on the Rev 3 video, I decided not to use it any more.
One thing I would add, though. If you are paying $50 to $80 for a sheet of rubber, I would humbly suggest that the cost of the glue ought not to be a factor (since costs of even the most expensive TT glues are trivial compared to that). The only factor should be that the glue performs the way you want it to for whatever is most important for you, and I think everybody would agree that the most important thing of all is that you want it to attach the rubber in a way that does not in any way adversely affect the way it plays.
And once you find something that works for you -- again your technique is part of the thing -- don't spend a lot of time changing.
So there is no one correct answer as to what is the "best glue".
