Reading GPIO on TM4C123G board
Choosing pull-up or pull-down for an input pin is a good idea if it is connected to a signal that can become tri-state / disconnected (like switch). In this case an input without a pulling resistor will have an undefined value. If it is pulled down, it will have a value of 0 when disconnected. If pulled up - it will be 1. As for the strength, it depends on your tradeoffs. Generally, the lower currents - the less energy you circuit consumes and cooler the components are getting. But if the pin should source/sink a higher current (to drive a LED, for example), it should be set to the appropriate current value. For the Input pins there is no effect of the strength parameter. As from the TivaWare driverlib user guide:


  For pin(s) configured as input ports, the pad is configured as
  requested, but the only real effect on the input is the configuration
  of the pull-up or pull-down termination.