I've worked for a few of the larger PM companies and the industry standard seems to be 20% discount if you are choosing to live there, 100% discount if the job requires it.

This is mainly due to the tax code which counts anything between 20% and 100% as taxable non-cash income. Some companies offer tiered discounts based on position. For example, as PM I've had up to a 60% discount, taxed on 40% of it.

Depends on the ownership and how the company is held. I have a publicly held client who is comfortable with 50% and one who is only comfortable with 20% due to tax filing. Private owners tend to be more flexible (IMO). Also, some states (CA) require an associate to live on site if the site is more than a certain number of units (16 in CA), whereas other states (AZ) doesn’t have this requirement. Some owners feel banks generally only give credit for 95% occupancy so many offer free apartments. Some sites may have different needs as it relates to staff presence. Some prefer maintenance to live onsite in case of a maintenance emergency and others prefer managers. Some don’t care what position as they recognize the value of associates living onsite and having pride and/or ownership to where they live. It is certainly not a one size fits all. Probably doesn’t give you the definitive answer you may be looking for.

20% FT & 10% PT - same as above. 

Our maintenance on-site personnel have one flat rate, but on-site property managers have a different rate based on occupancy of property for a certain amount of time, i.e. they start at one rate, and earn higher rate discount as occupancy goes up and stays, up to a certain percentage. 

20% for FT employees
10% for PT

We have seen position based (1 or 2 maintenance and on-site PM is fine) and give a 10% discount but the expectation is that they also respond to some after hours emergencies.