I would go Earth/Psi, it plays just like the potent Fire/Psi combo.
Well, don't the stone cages stop knockback? That makes you able to control when or when not to knockback targets with TK thrust on the earth/psi. *shrugs* If indeed that matters.
The Mind/earth gets four holds, on a toggle, with powerboost. that makes in very possibly the king of ST control.
Other than that, /Psi seems slightly better for range/AOE, while /earth wins out on its ST close damage.
Stone cages do indeed stop KB.
I eventually decided to do both Mind/Earth and Earth/Psi. Why have one character when you can make two? 
I haven't played the Earth/Psi much yet, but the Mind/Earth is an extremely good soloist, especially against mez resistant lt's and bosses (largely due to the ST sleep being mag 4).
The one gripe I've had about the Mind/Earth is that he is VERY single target. Granted, Dom's aren't meant to necessarily be AoE monsters, but Earth Assault's ST focus is very noticeable. I have Tremor, but the damage from it is laughable, to be honest.
I'll probably try leveling the Earth/Psi soon. I like the amount of AoE control you get from Earth Control, and Psi Assault has a little more AoE in it than Earth Assault. Should be an interesting pairing.
I've had an idea for a character that I just can't get out of my head.
His concept would be accurately portrayed by either Mind/Earth or Earth/Psi.
Problem is, between those two combo's I just can't make up my mind. My thoughts are the Mind/Earth would be more solo friendly (especially at lower levels), and Earth/Psi more team friendly.
Is there anything I'm missing? Any particular synergy that I'm overlooking for either combination?