From North to Taitung - which way is the quickest

what is the quickest way to travel to Green Island, except for flying? We are considering a road trip from Hsinchu (Xinzhu), I was wondering whether it is faster going all the way down to Pingdong with the highway and cut over the mountain to Taidong, or is it better [faster] to go round the East side of the island? Any ideas?

yep, by far quicker to go down the west coast to pingdong and then across and back up (bei hui - i think that is the name of the road)

if you have more time then going over the southern-cross island highway is a nicer route though.