Which Pokemon to power-up?

Hi, can anybody help me to understand which pokemon I shold power up all the way?
I am level 37 and have a few very strong Pokemon. I have quite a few pokemon with good IV, yet I don’t know which ones to power up.
It seems that only a handful of them, can actually go above 3000 CP, yet when fighting against Giovanni I’m very limited with the types.
So my question is: If I have Metagross (psychic/steel), does it even make sense, to power up an Espeon (because it’s also psychic)? Or is the attack completely different due to Bullet Punch on Metagross and Confusion on Espeon?
Should I rather power up another type, even though it can’t go beyond 3000?

Some Pokemon with 2 types only do well in a single type: take Venusaur. It’s an excellent Grass attacker with Frenzy Plant, but is never used for Poison offense because it has no Poison fast move. Some, however, excel in both types, like Metagross: with Zen Headbutt/Psychic and Bullet Punch/Meteor Mash, it can do well in both Steel and Psychic offense. For the case with Metagross/Espeon, if you need to save dust, just invest in Metagross and get it a second move. However, if you have dust to spare, best to note that Espeon does better Psychic DPS than Metagross.

Also, you put the topic in the wrong section. Might as well move it to the Pokemon Go section.