Ylan - Hualien
Best East coast ride for me. It starts with a straight flat road along the valley, then gets serious with 2 steep climbs, hardly met any cars in 2 hours. the views on the ocean are amazing. The rest of the ride follows the coast with another climb and quite a few tunnels, some of them half open to nice views to the sea.
Note that most people complain about the heavy traffic, mostly from trucks. This is true, but only comes at km 28, when road 9 joins road 9 bis, the one you follow on the bike. Still, apart from the deafening noise, trucks are very much aware of cyclists, so with good lighting, no problem.