I've been using Camelbak 3L bladders for all of my outdoor activities for decades and haven't had any issues. Granted, if the plastic taste comes about when they are new, then perhaps I've long forgotten about that detail. I often leave water in the bladders by accident for weeks and after dumping out the old water (may be a bit slimey), I still don't notice an off taste. Back in my firefighting days we used Camelbak bladders, and let me tell you, those things were so nasty. They picked up the smoke from the fires. The MSR Dromedary has been mentioned, and I have successfully used the Lite one for backpacking, but that little black nozzle gave out and soaked my whole pack once. The replacement solved the problem. The black Dromedary bags are super thick and durable, and shouldn't ever leak.
My most valuable advice: DO NOT buy cheap gallon jugs of water and throw them in your pack. I tried that once with 6 gallons of water from Walmart when I was backpack hunting (in AZ) and damn near every one was popping its lid or had pinhole leaks in the sides. Won't be doing that again...
Oh, and an odd thing that a couple of my hunting buddies do is carry around fresh disposable 12oz bottles of water. Of course they conveniently crush the empty ones when I'm trying to be stealthy. I most certainly don't advocate this approach.
