Burr Brown or Wolfson

I have heard both, as well as Crystal too.

There's more to a CDP than just the chipset to get to the end result- the converters play a big part, as well as (but maybe not as significantly) the build quality.

That said, for budget high quality sound, I really like what Cambridge Audio accomplishes with Wolfsons in the 640 (which I own) and 840 II (which I adore).

Ps- I've heard modern CDPs with Crystal and Burr Browns too, and if the player is of reputable quality, they work fantastic too. Lots of great CDPs using all three brands of chips.