Which would be better to see if you could only travel to one in March? How many days to give a good view of the area. Thanks
The Amalfi Coast would probably be a better choice in March, as the Cinque Terre doesn't fully open for the season until 1 April. There will probably be a few places open, but if the weather is "inclement", it won't be any fun. The Amalfi Coast will likely be a bit warmer in March.
I vote for Amalfi coast for the same reasons as Ken. It is farther south.
Weather aside, which is likely to be similar, the Amalfi Coast/Gulf of Naples area has many more things to see and do compared to the Cinque Terre.
Amalfi Coast for all reasons listed so far.
Amalfi coast, unless you like cooler temps, the possibility of inclement weather and towns that are for the most part shuttered for the season. As I recall the Amalfi is pretty much active all year. Also if the weather goes south, there are some good indoor activities in Naples.