SAR vs. Delta-Sigma ADC
For your application, either should work fine, but generally, an SAR ADC can run with much less power consumption than an Delta-Sigma, and most common SAR converters enter an almost zero power state unless the input changes.  Under 2 or 3 MHz, I probably wouldn't even think of going with a Delta-Sigma converter.  SAR's also need less signal conditioning on the front end generally.