Both USB and ESC power options
Given that the 5V supplies are feeding a 3V3 LDO, then why not just use two Schottky diodes. 

Put one in series with each supply. That will allow both to work, and the higher voltage will 'win'. Schottky diodes will only drop 0.1-0.2V in conduction.

Here is a 2A one I use often:
http://www.digikey.com.au/product-detail/en/CDBB2100-G/641-1109-1-ND/1559070