so im making a echo knight/genie blade pact warlock

i took eldritch blast for long range, booming blade (plus crusher feat) for close range, and echo for everything else.

but i am stumped on what my 3rd cantrip should be.

char is a bugbear using a maul w/ crusher feat. max charisma, +4 str, rest of stats are meh.

invocations = mask of many faces, misty visions, improved pact weapon, and agonizing blast

what do ya'll suggest for my 3rd cantrip? 1st session with the char is tomorrow

Damage variety is probably less likely important than spell variety. Minor illusion or prestidigitation are probably the best choices.

Blade ward and True Strike are too weak to be worth the slot, generally.

A spell save DC cantrip seems like what you'll get the most use out of. You're pretty well covered on a lot of utility... the only thing that might slow you down is facing off against a foe who has crazy high AC. I'd probably go for Toll the Dead, for sheer damage output, or Frostbite for that disadvantage on the target's next attack. Most creatures with high AC usually hit pretty hard too, so that extra defense could be a big help. Mind Sliver is also a solid choice, especially to help set up a combo for another player. I think Lightning Lure might be worth it for a melee-focused character, but it's relatively short range and doesn't output a particularly impressive amount of damage... I think you'd have to build around it, but it could be more "fun" than some of the other options.