Gardevoir - Confusion or Charge Beam

CB/SB Gardevoir has a current, niche use against Lugia. Aside from Lugia, though, I'm not sure there are as many uses for CB relative to Confusion. And, Confusion is better for gym defence.
My only Gardevoir started off with CB/SB; I FTM'd to Co/SB, and it ended up being one of my MVP's against SP/SB raid boss Gengar - but only b/c SB is easy to dodge.

I love confusion on my Gardevoir. I don't go into battle without her except raids. As for CB, my zapdos has it, I think it's about the same speed as confusion. The only reason why Psycho Cut is comparable confusion on Mew2, Espeon, and Alakazam is because Psycho Cut is very fast, but Charge Beam is not that fast to be compared with Confusion. If you have extra TMs, I suggest you try both in battle and see which you like.

charge beam doesn't have much (if any) synergy with dazzling gleam.

charge beam's dps is mediocre so its only use is to allow you to use your charge move more frequently to make up for the lower dps.

fairy is super effective vs dark, fighting and dragon, but against these types there's usually a better counter than fairy. vs dark types, fighting fare better as they resist dark moves while gardevoir takes neutral damage, and in the case of tyranitar, it is also double weak to fighting.

vs dragons, several of them have a double weakness to ice making ice pokemon better counters, or dragon types themselves as they'll have better performing movesets (e.g. the standard dragon tail + outrage).

even if you do want to use gardevoir vs dragons just because, confusion + dazzling beats charge beam, at least in rayquaza sims.

and finally vs fighting types you'd want confusion as it's super effective. pretty straight forward.

Confusion. I used Charge Beam against Rayquaza because it made dodging easier and felt like it often gave me an extra charge move during the lifetime of the Gardevoir, but TM'd back to Confusion as soon as those raids were over. It's overall much better.