Knowing what the default terminal emulator

There is no standard for knowing what the default
terminal emulators is across distros.
You would only be able to guess it by looking into
different system variables and config files.

terms=(emulator1 emulator2 emulator3)
   for t in ${terms[*]}
   do
       if [ $(command -v $t) ]
       then
           detected_term=$t
           break
       fi
   done
echo $detected_term