A good landlord is one who is active towards solving his/her tenant's rental issues quickly, treats the tenants with respect, regularly asks if there are any problems with the renting unit, and helps the tenants in settling down during the early days of moving in.
A good tenant is one who is honest and trustworthy, does not disturb his/her neighbors, follows house rules (e.g., no smoking, no pets etc.), pays the rent on time and maintains the property well.
A bad landlord is one who harasses or steals from his/her tenants, damages the tenant’s property, is not actively responding to requests for repairs and/or maintenance, treats the tenants with disrespect or discrimination, never asks if there are any problems with the rental unit, and does not solve problems quickly.
A bad tenant is the one who steals from the landlord, damages the rental property, withholds the rent without reason, is disruptive not only to the landlord but to the neighbors as well.