If you believe in blanks making a difference in sound, TDK's XA-PRO is the best; its shell is at least double the weight of most cheap MD blanks, and that makes the difference. I have friends who didn't believe in blanks making a difference until he heard the XA-PRO.
You don't believe in that? I don't mind.
In either case, it seems that the XA-PRO production has ended.
The hierarchy for the Japanese brands goes:
Sony MD2000, TDK XA-PRO (pretty much tie, but priced very differently)
Sony ES/Professional (same shell), Axia Pro
Maxell Music Gear (formerly Pure Platinum/Gold), Sony Prism
all the color ones, Neige, Maxell SX
Several "relatively high-quality" blanks are no longer in production, like the Maxell XL and the TDK XA.
In Japan, you'd often be able to buy the "number 2 class" blanks (Sony ES, etc) for the same price as the cheaper blanks, so while they're good quality, I don't see any reason that you're charged more than a couple $ extra for them.
An instant benefit of the ES is that you can write on the shells in pencil, and also pretty much rub them out with an eraser. If you're looking for higher quality stuff, the ES wouldn't be a bad choice, given that they're not priced too differently from the basic blanks.
I'm currently using: TDK XA-PRO, Maxell XL, Maxell Pure Platinum, Sony ES, Sony Prism, Sony Neige. My personal favorite is the Pure Platinum; I think it's ES-class but I'm not totally sure.