I understand the basic use of a pull-up or pull-down resistor, including the specific case of using it with a tact switch.
When both are an option I was wondering whether I should favor one over the other and if so, why?
Some times you can gain a reduction in current by choosing one over the other. For a momentary switch this would not be the case.
If all other things are equal I would favor a pull-up resistor. Some microcontrollers (like the Atmega series) have inputs that can be configured with an internal pull-up. Using only pull-ups (internal or external) does provide some consistency.
One advantage not yet mentioned for using pull-ups rather than pull-downs is that when using a pull-up, one end of the switch must be tied to ground; when using a pull-down, it must be tied to VDD. Exposing ground or VDD means there's some possibility something else might get shorted to it. Generally, shorting something to VDD is apt to be more damaging than shorting it to ground. Further, exposed connections run the risk of electrostatic discharge; discharge into VDD is often more damaging than discharge into ground.