I would recommend selling off anything that gives you debuffs such as pant pant: https://dblegends.gamepress.gg/equipment/pant-pant and sacred water: https://dblegends.gamepress.gg/equipment/sacred-water (which has a chance of randomly giving you debuffs.
outta the way: https://dblegends.gamepress.gg/equipment/outta-way is also pretty weak and useless, so you could sell that one if you're really strapped for space.
My personal rule is to only keep the strongest 2 or 3 of a single equipment after it's fully upgraded and sell off any E grade equips without bothering to upgrade them.
Hope this helped ^_^
