Getting away from DPR, Vicious Mockery only does d4, so it's average damage is 3 points per die lower than EB, but it's psychic which is also rarely resisted and it grants disadvantage on the next attack, which is a pretty good debuff for a cantrip. And really, if I'm throwing cantrips I'm not pretending to keep up in DPR anyway (with the exception you already noted of warlocks with invocation and hex).

Sliding back to damage and seeing if it still wants to date, while EB is probably the top general performer the equation changes a bit if you can boost a damage type. For example with the Aasimar in Volo's once per day for a minute you can add +level to radiant or necrotic (depending on subrace) damage once per round. That makes Chill Touch and Sacred Flame really nice. Dragon Sorcerer at 6th can boost a damage type depending on dragon color which can also give you a different winner. UA has the Undying Light Warlock that adds +Chr to fire and radiant damage for those cantrips, so you could use firebolt for d10s or sacred flame for d8s and ignore cover radiant without spending an invocation. Fire is pretty easily resisted, but radiant isn't and has a bunch of creatures vulnerable to it. Plus Sacred Flame ignore cover.

If you have 2 or more adjacent opponents, Sword Burst from SCAG beats EB without invocation. It's d6s to all adjacent, also force damage.

All of this is assuming pure cantrip damage. If you are a reasonable with a weapon and don't mind engaging, the SCAG cantrips Booming Blade or Green Flame Blade can deliver more damage since they also have weapon damage in there. Nice for use with a melee but single attack character like some rogue, clerics, or the UA Mystic (Immortal).

Oh, as a side point if the cantrip you are looking at is on the Wizard list, you can also get it by being a High Elf without spending a feat. (Or half elf with the SCAG option.)