A small pack of pleuro's would be my choice for that sized tank , 180 has lots of room for them to move around .
Would be over kill for asiatica or obscura but extra space won't hurt them, Same goes for Auranti mine were raised out in a 4' 110 it was a perfect size . They live in a 160 now but only because if leaves room for their offspring , the rest of the year it's way more space then needed and looks empty lol.