SAR : good: Most popular in industry now.
good: find a job for future is easy because you has SAR ADC circuit design experience
bad : can only learn fast comparator circuit skills and capacitor mismatch calculation
does not has high performance Amplifier circuit experience
Pipelined : good : can learn much more circuit skills include:
common mode feedback , high perofmrance differential amplifier,charge
injection skills. Once you has designed a pipelined ADC done. you will find
other circuit is more easy than to design a pipelined ADC.
bad: industry does not use pipelined ADC recently.
sigma delta ADC
Good: most popular for high resolution requirement application.
Good: if you have done a good sigma delta ADC, you will get a good understanding about the signal/noise/sampling/frequency domain and time domain transfer. Easy to get a job.
Bad: for high sampling rate, it is not easy to implement. The power is not low enough for some low power application.