Dominate recharges faster, activates faster, does damage, lasts longer, is a stronger control, and is more accurate.
End cost is comparable.
Scramble thoughts has longer range (~20yds).
They're both pink on your power tray, but scramble thoughts is less garish and has a slightly cooler icon.
DON'T eat muffins while I'm developing you.
Pants! Turkey Magnates! A man in a box! Rogue AI! Come one, come all, to arc ID 10107 - It's [i]'Not as long as some other arcs'[/i]!
Mainly because your empathy I'll suggest Dominate. Scrambled thoughts takes too long and is weaker in almost every other way but perhaps its better for PvP as its a disorient. Dominate has the right amount of range because its more similar to the ranges of your empath powers anyway.
He will honor his words; he will definitely carry out his actions. What he promises he will fulfill. He does not care about his bodily self, putting his life and death aside to come forward for another's troubled besiegement. He does not boast about his ability, or shamelessly extol his own virtues. - Sima Qian.
Thank you for your responses. Sounds like Dominate is the way to go.
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They're both pink on your power tray, but scramble thoughts is less garish and has a slightly cooler icon.
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I can't tell you how much I loved this line!
Agreed - Dominate is better than scramble thoughts. I had both on my kin/psi defender - and after many different respecs, have finally rid myself of scramble thoughts. As Wilfred said, dominate recharges faster, does more damage (I've got mine slotted with 4 damage procs, so it can do wicked damage!) and activates faster than scramble. However, as Shannon pointed out, scramble is a disorient, not a hold - so it can be useful for blasting those pesky bubblers (who have resistance to hold with their bubbles, but not to disorient) and characters with acrobatics (gives some resistance to hold but nothing to disorient).
So it all depends on your style of play: PvE - definitely dominate. PvP - there's argument for scramble thoughts (though personally, I'd still take dominate) 
Hope this helped to make it clear as mud
Definately 'Dominate'... without a shadow of a doubt in my opinion. It can be quite nasty slotted well and its my opening salvo along with Will Domination - With regard to PvP; I've heard screams of "H4X!" when its knocked off Masterminds Personal Forcefields!.
Thanks for the advice.
My PvP experience usually only ever involes me teleporting wildly around bloody bay doing the mish to top up my temporary stealth powers. If I accidentaly teleport within buffing range of a hero i'll buff and then head straight back to the helecopter so PvP effects aren't a big factor.
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However, as Shannon pointed out, scramble is a disorient, not a hold - so it can be useful for blasting those pesky bubblers (who have resistance to hold with their bubbles, but not to disorient)
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Bubblers are resistance to stun as well. Will dom should be your first attack vs a bubbler, really
I'll shortly be coming to the point where I will be taking either Scramble thoughts fom psi blast or Dominate from psychic mastery (mid 40's emp/psi defender).
Quick question is - which do people think is better as they don't seem much different to me on first looks. All opinions welcome.