There was a big discussion on this topic about two weeks ago on the Sample Libs forum. Everyone wants 24-bits, but not everybody agreed about the sample rate. My feeling is that it's best to use the target rate (e.g. 44.1 kHz for making CDs). Spectrum mentioned that he dislikes all of the downconverters that he's heard. When he has to downconvert, he plays out to analog and recaptures to digital at the required rate through high-end A/Ds and D/As.