The best way is by ear, as long as it is sophisticated enough to handle ANYTHING you throw at it. The trick here is, unlike what some are saying, it is NOT a gift, but something that can be taught and trained... While I was at music college, the first 30 minutes of every single day there was spent doing aural exercises. No pen, no paper, no nothing, Interval recognition, chord recognition, melody repetition, singing back what one heard, interval singing... These kinds of things can be vastly improved by practice.

Yes, I had a fairly decent ear going in to college (had some of this while I was at high school, and some of it WAS innate), but those years of sharpening my ear up first thing in the morning, I honestly believe, were possibly the MOST useful thing I ever got from attending college (this was an all classical college, no jazz or pop curriculum, so only technique really was useful when I went off to make a living playing popular music).

Reading is a double edged sword, particularly in pop music. If you want to be a session player, or work in larger, more formal outfits (pit orchestras, bigband, show backing, etc.), you MUST read, but the worst thing is if you ONLY read. Written music is only a GUIDE to playing well. It cannot truly tell you how to play something, it is just a shorthand for the notes and approximate timing and feel, that YOU have to interpret and make better. If you play any pop sheet or chart EXACTLY as written, it will be horrible

So, unless you CAN play by ear as well, knowing charts only gets you half way (barely!) there...

Trust me on this one, guys. If you can't play by ear, and resort to rote charts to get you through, don't give up. You CAN develop the skill of playing by ear. BUT.... it takes time. Just as you spent YEARS learning to play the piano well, it takes a long time (depending on how hard you practice) to train your ears up as well. But the rewards are MORE than worth the effort. You weren't born a great player. You had to work many years to get where you are. Put that kind of time into ear training (and it will pay off from day one) and after a while, you won't need your charts at all.

But at least you'll be able to read them when you DO need them...