R2R operates on a principle of switch resistors network and there’s no feedback loop to do the correction. Therefore R2R requires good matching to get good linearity. Because it operates in full set of bit range, e.g, 24-bit and does not require any form feedback loop to do the correction, the results is better time response and does not require noise shaping circuit. R2R DAC is inherently very quiet.
Sigma delta 1 bit converter operates in a feedback loop constantly correcting itself from errors. The delay of which feedback loop keeps correcting itself from errors has a great impact how fast these converter can response in a time domain. Because it operates in 1-bit fashion, it requires noise shaping to push the noise away from the audio band. Sigma Delta is quite noisy considered if one open up the whole spectrum of frequencies.