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It depends on application requirements and acceptable cost metrics. There is no one-size-fits-all solution as there are trade-offs between speed, accuracy, power consumption and area. For example, a portable audio device requires relatively low bandwidth, high accuracy, low power consumption and cost-effective area. These traits enable a high clarity audio experience that preserves the original sound of the recording, a long-lasting battery life and a competitive end-product prising for mass market. On the other hand, communication equipment such as base station receiver will benefit from extreme bandwidth and moderate-to-high accuracy. While also important, the power consumption and area might not be that critical since these are mainly limited by thermal performance and unit size.

SAR (serial approximation register) ADC is best suited for application that requires moderate accuracy and low power consumption. Bandwidths go up to several hundred of MHz in modern processes, and they are also applied in extreme bandwidth systems by time-interleaving several identical SAR ADCs. Achieving >12bit accuracy in all conditions requires extensive calibration efforts. Sigma-delta ADCs on the other hand are best suited for high accuracy and low to medium speed applications. The bandwidth is limited by the required oversampling. However, the advantage is that the quantization noise and other non-idealities of the key circuits are shaped out of the bandwidth of interest, making the performance less dependent on calibration. When targeting accuracy of >12bits, the sigma-delta ADC is the preferred choice if speed is not a limiting factor.

Depends on the application. Integral nonlinearity (INL) and differential nonlinearity (DNL) measure how well the ADC or DAC work for DC or very slowly varying signal. They do not necessarily include any information about what happens with an input signal that has frequency close to the Nyquist frequency. For dynamic signals, it is better to use signal-to-noise ratio (SNR), signal-to-noise-and-distortion ratio (SNDR) and spurious-free-dynamic range (SFDR) to evaluate the performance.

In general, no. The number of physical bits poses only a limit for the performance; it does not guarantee it. Non-idealities, such as thermal noise, jitter or distortion can limit the performance to below what is expected from the number of output bits.

ENOB or effective number of bits basically answers the question what the signal-to-noise-and-distortion ratio (SNDR) is if an ideal Nyquist rate ENOB-bit ADC is used to convert a full-scale sine wave input and vice versa. The relation is defined as ENOB=(SNDR-1.76)/6.02. For example, an ideal 10-bit converter has maximum SNDR of about 62 dB.

An ADC can have a higher ENOB than the number of physical bits if the ADC utilizes oversampling, such as in delta-sigma ADC raw output before decimation. In that case, the SNDR is defined for a bandwidth that is less than half of the ADC sample rate (Nyquist rate). Only a part of the quantization noise is integrated when calculating the SNDR, which means ENOB can be higher than the number of physical bits.

Yes, IP can be adapted or designed for the target process and application.