What MCU, need hi res ADCs?
If you REALLY require 14 bit resolution then doing conversions on the MCU is probably not a good idea.  Maintaining signal conversion to this sort of accuracy is not a trivial undertaking.

Highly sensitive analogue circuitry on the same silicon as the MCU with all its clocks and associated noise sources is not a good combination - that is one reason why most MCUs have 10 or 12 bit ADCs.  Another reason is that the silicon process used for the MCU is optimised for high speed digital signals.  This process does not work so well for high accuracy analogue processing.

If you are wanting to process analogue signals to this level of resolution then you should keep the analogue signals away from the digital sections, with their own converters, low noise reference and quiet power supply rails so that you do not add noise to the signal being analysed.

Remember, if your analogue signal has a peak value of 1V (corresponding to adc full scale) then each bit is only 60uV.

In addition, you really need to have a handle on your power supply and might want to consider a separate supply for the analog side and the DC side.  It might be overkill if your supply is designed right, but if not you could easily have several "bits" of discrepancy due to voltage ripple and the micro and other components making small but meaningful changes on the load and the supply voltage of their own.  Remember, the higher the resolution the larger those fluctuations are.