Appropriate ADC for educational project?

Nonlinear coded AD/DA has been used in early days of digital voice processing (e.g. with the µ-law codec), but it's long gone. SD ADC are linear by it's operation principle, also any kind of digital signal processing (e.g. decimation, filtering, FFT) is based on linear coding. If huge dynamic is involved in an application, it may use dynamical gain switching and a respective floating point data representation. But it's surely not required for voice processing. I would assume, that a resolution of 10 or 12 Bit is sufficient for your purpose.