Actually, a number of different brands each have excellent features that none of the others do.
Blackburn has the only mouthpiece that honest-to-goodness is easy to open with just your tongue but never leaks when closed, Blackburn also holds the most water and is easiest to fill all the way to the brim. It's pretty light for the amount it holds, too.
Ultimate has the only one which is honestly easy to clean inside. Ultimate also has the least slosh. Ultimate also has the best way to hold the tube in place near your mouth.
Osprey has the pack which rides most comfortably and stays closest to the body.
Platypus and Gregory have the lightest bladders.
Blackburn, Ultimate, and MSR have the best Durability.
Blackburn and Ultimate let through the largest water flow.
MSR has the best versatility.
Blackhawk has the pack with the most features. (Frankly, this is worthless for most real-world use. You either want to travel super-light, with something more minimal, or you want to throw your water bladder into your regular backpack, which is more full-featured and better designed.)
Camelbak has a real popular name brand and high price to impress everyone.
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So, in this sense, there is no single best. (Except Blackburn.

) You need to evaluate which features are most important to you, and buy accordingly.
Also, remember that (if you have the money and the need) you can use the mouthpiece from one, the tubing from another, the bladder from another, and the pack from another.
--Mike