Bear in mind that each one only gives 1 emerald; thus, over time, it's more efficient to go with the shedding method as each villager can theoretically shed multiple times even if it takes bloody forever.How is it that you "smelt villagers"?
I really need Emeralds
At first, you'll probably get nothing, but eventually, with enough villagers crammed into range of the vacuum chest you should get a steady trickle of emeralds.