Sigma Delta ADC vs SAR ADC, for multiplexing signal
I'm not sure why no one brought up the STM32F373 with THREE 16bit Sigma-Delta that can do simultaneous conversions  at 50Ksps single or multiplex them at 16.5Ksps(21 single ended channels or 11 differential channels), plus a 12bit 1Msps SAR ADC.  ST has a App Note about using it for a power meter and they use the SDADCs for current and the SAR ADC for voltage.  It has floating point + DSP at a 72Mhz.  Plus 2 12bit 1Msps DACs, 2 RR analog comps, 15 timers, USB, CAN, etc.  All the ADCs can be triggered from the same timer/source.

I'm using one to make a LCR/ESR meter.  Right now I'm trying to see if I can use one of the DACs for the excitation voltage or have to go with an external DDS.