The best one on the market today?
It's no longer in production, but the highest recommended one I've heard of is the Sony D-555. That said, some of their newer, less "audiophile" players like the S2 series have absolutely mindblowing skip protection.
C. Taylor! I was just about to mention the same player.
The Sony D-555 is the bomb. I still have mine.
It was more fun than any other protable model, ever!
I also agree with Mr. Taylor in that it is best used "sitting still."
If portable means able to travel easily, this one is killer.
If you need it for jogging or activity, then this is too bulky and not shock resistent enough.
P.S. They often go for under a hundred bucks on Ebay.