Inferno won't work up close, but it does have one more advantage over Arrow Rain. It is a ranged attack. It dramatically cuts pot costs when used correctly (especially in unison with puppet). Later on, the burn effect isn't as important, but when doing mid-level training (90-120), it is a very nice boost. Eventually, you'll kill mobs too quickly to notice the burn effect, but currently it can really help rack up damage. One technique I liked to use (especially at peak) was puppet mobbing:
You aggro a group of monsters by attacking them all. You'll know if they're all aggroed by the burn effect. Continue around the map aggroing mobs. Finally, when you get to a corner or edge, throw up puppet (try to place it out of harms way if you can...if not, it will hold up for a while still). Let the monsters attack the puppet in a giant group while you spam Inferno on them. The damage really adds up, and you use very minimal amounts of pots.