Agave is sweeter than honey though not as viscous. (You'll find the dark agave nectar has even more depth.)
If it is just sweetness you seek go with the agave. Start with less then add more, if necessary, to taste. It mixes into other ingredients more easily the honey.
If it is the distinct (and distinctive) flavor of honey you seek use it - or use a combination of the two, agave for the basic sweetness, honey for its flavor.
Honey's flavor is practically destroyed by heat. If its flavor is key to the results of a finished item, a sauce say, add it after the sauce has cooked and is removed from the heat (and allowed to cool a bit).