I would look at the use case for your existing MR16s and the current and likely future usage profile for the replacement APs.   Like others, I'd question the use of MR20, particularly for its lack of 3rd (scanning) WiFi radio.  It may be the closest in terms of capability to the MR16, but if you're using those APs for serving a modern carpeted office, with the usual for example, I'd actually use MR46 as my 'vanilla' starting point.   If this can't be justified, cost-wise, then MR36. ... View more