See pic below for example...
Hope someone can point me in the right direction
Just using the Named Control in your formula will result in the value of whichever field (Drop Down -or- Fill In) is currently selected.
You can see this easily simply using the Named Control as the formula for a Calculated Control, and looking at the output.
(Naming a choice control)
(Adding the Named Control reference to a Calculated Control's Formula)
(Showing the value when an option is selected and active)
(Showing the value when the fill in is active)
So, as shown, using the Referenced Named Control of the Choice in question will always result in the correct value being passed to your Rule.
NWF$("#" + optionsID).siblings(".nf-choice-control-radio-button").find("input").prop("checked")
will tell you whether or not the top 'Default Choice' control is active, but again, how you use that is entirely up to how your rules are set up.