Best Airgun Brand?

Well to truly be fair I would want to have extensive experience with all the top brands but that's just not going to happen. Best means different things to different people. You might want to pick a category such as best 10 meter competition gun or best bench rest competition gun or best hunting gun or? Its likely that the best in one category is not the best in another. Some company's only make competition target guns and have no hunting guns. Some the other way around. What about big bore? Does Styer make a .50 cal? Me? all I could do was lots of reasearch and I came to the conclusion that the Rapid Air Weapons HM1000x in .25 was best for my wants/needs/taste. YMMV.

"Best" ....well, that is very much relative to needs and applications.

What might be Best for one person might well be way down the list for an other.

Personally, based on my limited experience in airguns, I think they are similar to cars...doesn't matter what the brand, you can always get a lemon. Based on my one FX (Revolution) which has been a remarkable accurate piece of reliable engineering to me, I know that other owners believe it to be a piece of junk that should have never been made due to jamming and unreliable semiauto operation. So to me, FX is the top based on my one gun experience. I also think Evanix makes a fine and powerful airgun for the money based on the Max ML that I own but again, have read other owners who think they are junk. I am very interested in Steyr as I know they make high quality firearms and imagine their airguns are no different so they would be my guess as general best quality, workmanship, etc.

Depends on what there used for ...
The higher end guns that I have are.... Steyr, FWB, Daystate, RWS, HW, Beeman 
I have an FX Impact on order but as of today, IMHO
"BEST" for hunting, Daystate
"BEST" for target, Steyr LG 110 ... though my AZ tuned FWB P-70 is a VERY VERY close second
"BEST" for general plinking, My Daystate Mk4 

I have shot many airguns and found when you are at this level the quality for the most part is there, and it becomes a personal preference thing.

Crosman! Has there ever been any doubt?

Crosman, according to Predator Xtreme readers (three years in a row)
Game & Fish / Sportsman Magazine readers say it's Benjamin 
A global survey by Fieldsports Channel put Crosman at the top

LOL.
Few have enough experience behind enough guns to say.
I also don't think there is a clear cut winner.
AND.....as has been noted, needs/desires differ.
I will say my next one will be it.
Good days to be a air gun aficionado.

Best is what fits your budget and needs. Accordingly the Marauder 25 is "Best" for me.

Daystate has the most beautifully finished guns I've ever seen.

Most expensives ones are 

Beamont
Corsair
Drummen Sinner

They all start at 3000 (euro's), up to 5 or 6, or even 7000 (10.000 dollars?) 

You are the only one to decide. Even if we could determine the most accurate rifle, would it be too heavy for you to carry around? Would the caliber be too great for the distances you anticipate shooting at? Are you completely uninspired by synthetic stocks, only Italian walnut for you? Long rifles too bulky, you need a carbine? Loudness, is that an issue? Lucky you, having the cash to make all your preferences a reality. But it doesn't get you out of committing to those preferences from the start. Good luck to you, Im sure whatever you choose will be outstanding. But only you can say if its the best. 

I have a few Crossman Marauders but I just bought an FX 400 FT and in my humble opinion, it is the best gun for ME. I looked at all of the Styer, Daystates and AirArms guns. When it came down to it, the FX worked best for ME and filled all of my needs. 

Good luck making your decision.

Jamie