Tech Thrash easily, with no competition.
 
Sadus, Watchtower, Later Destruction, Antagonist, Hexenhaus, Depressive Age,  their aren't many bands, but Hell their original

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Yeah man, Coroner and Nasty Savage are bad ass too.
It's a close call for me, I like alotta technical Death Metal too (when it's done right). Psycroptic, Hellwitch (the underrated godfathers of technical death), fleshgod apoclalypse, and Hour Of Penance

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Shit yeah!... Shit no, No One likes shit!

Is Technical Thrash similar to speed thrash?
 
I don't know alot about Thrash Metal

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I remember having fun once, it was terrible...

Hell yeah, Destruction are amazing, probably one of my favorite bands of all time.
I don't know much Technical Thrash bands, that Means besides of Nasty Savage. Any suggestions?

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Tech death wins for me. Every Death Metal band from Québec are pretty much tech death, and I love them all. Cryptopsy (old), Neuraxis, Gorguts, Quo Vadis (favourite), and Martyr. For elsewhere, then there is Fleshgod Apocalypse, Portal, Necrophagist, Death, Origin, and the list can go on.

The only technical thrash bands that I truly like would be Strapping Young Lad and Sadus.

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Last.fm: Mercenarion

@DemoGoreFest, nice Nasty Savage, and Hellwitch mention. and for tech thrash I Forgot to add Toxik, and Vektor
 
@Mercenarion, ye I like Quebec tech death because it has alot of progressiveness, but Origin, and Necrophagist are redundant, for original tech death bands, you should check out Carcariass, Chemical Breath, Iniquity, Theory In Practice, Augury (one of my all time favourite bands, I got to meet them, and get merch signed while I was at the concert, fuck my neck Hurt in the morning it was awesome!)

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Carcariass and Augury (yay Canada!) are good, the others I have heard before and I do not care for them. On the point of the redundancy of those two bands I stated, sure Necrophagist can be redundant, but they are still very good. Origin never interested me until I heard Antithesis (the only album I like by them, but it is amazing).

I've heard you mention Theory In Practice (or heard it somewhere else), so I'll check them out.

EDIT: Theory In Practice are epic

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Last.fm: Mercenarion

I prefer more technical death, because I think it leaves more room to creativity somehow.

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I like Technical Death because I'm not really a huge fan of Thrash.

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I remember having fun once, it was terrible...

Apples vs. Oranges.

Both genres are miles apart but there's plenty of amazing stuff to be found in both of them. Realm, Obliveon, Watchtower and Coroner dominate techthrash for me whereas Quo Vadis, Neuraxis, (old) Cryptopsy, Ulcerate and Gorguts satisfy most of my techdeth needs. But at The End of the day, they both serve completely different purposes imo. Comparing them is a foolish prospect.