What's the most important gear to enchant, first and foremost?

Is it damage or is it defense? My sword got too expensive after enchanting it so much, and I'm still struggling on certain levels. Should I start upgrading defense next?

It depends on the stats of the items primarily. Defense is important so you take less damage. Some items increase the %'s of damage, health, crits... etc. Mostly you want some balance, and with the percent increases the values stack and increase on themselves giving you better values.

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