Immediately what comes to mind for me is Commander decks with a heavy Enchantment theme. This includes Daxos the Returned and the hated Zur the Enchanter, but also Voltron Aura-loving commanders like Bruna, Light of Alabaster, Krond the Dawn-Clad and Uril the Miststalker. With such a minimal commitment of mana, the Helm could deal those last few points of commander damage you need for the win. It can go on any creature, though. Any deck that loves enchantments can use it.
Also, Trinket Mage can grab it, being a one mana artifact. Being an equipment, Quest for the Holy Relic, Steelshaper’s Gift, Stoneforge Mystic, and Stonehewer Giant can also seek it out. You could get it with Relic Seeker from Magic Origins, too. So, Commander decks have plenty of ways to tutor for it, too.
Does it work in Constructed? Green/Black Constellation decks during the Journey into Nyx era could use it. Heroic decks could use it. But the Helm never really fit into those lists. Bogles decks in Modern could use it. But, again, it doesn't fit in what is already a deck vulnerable to dead draws. Modern Prison decks could find a slot or two and stick it on one of the few creatures in the deck. But that is hardly a top tier deck, and it's more like cute tech.
In Commander, it can fit because you have 99 slots to consider. In constructed decks, there isn't much give room. The decks in Standard when the Helm was released that use it to the best effect lost all of the Theros cards in October 2015. However, with the release of Dragons of Tarkir, SaffronOlive of MTGGoldfish came up with a Standard "Bogles" deck featuring Conifer Strider and Sagu Mauler. It used the full four copies of Helm of the Gods and was a fairly fun deck. But it wasn't a big winner or anything.
Still, Helm of the Gods can be an absolute killer in Commander. It's a card that gets better as you go. You just play it as soon as you need it. It could be a game-ender, and even a 2/2 boost is worth the investment. Unlike an Aura, it's usually going to stick on the board when the equipped creature is dealt with. Helm of the Gods' price may never make it a money card, but if a ton of enchantments are going to be in play for you, the Helm at least needs to be considered.