Using what we've been given from the show. Who do you think would win?

King Sombra, or Lord Tirek.

Sombra.

Because we see all that Tirek had to offer in his episode. Sombra? We don't know much about him. For all we know, he could possess COSMIC, PHENOMENAL POWERS!

Sombra.

3501176 Depends on whether or not Tirek can absorb dark magic. If he can't, Sombra wins. If he can, Sombra will probably still have the advantage because of stealth, but Tirek could easily drain him if he got the chance.

3501176 Both Sombra and Tirek use and I quote from Celestia, "Dark Magic." Yeah Yeah, I know that's a no brainer, but humor me for a second. What is dark magic? What do both Sombra and Tirek share in common when it comes to their magic?

They both absorb magic from an outside source. It is stated that Sombra gains power from fear and hatred. He is powered by these emotions. As for Tirek, he forcefully drains magic from others.

Now lets take a look at what we know from the show. Tirek was able to take on Twilight even after she had all the alicorn magic in Equestria, BUT that was only after Tirek had absorbed Discords power along with every other magical energy from the pony races.

If we compare it to Sombra, who fought both alicorn princesses of the time, Luna and Celestia, we can see that not only was he able to fight two powerful beings at once, but he also didn't lose. Sure he was banished, but if their goal was to kill Sombra and liberate the Crystal Empire, Celestia and Luna failed as they neither killed him, nor saved the Empire.

I am willing to wager that if Sombra had free reign and absorbed fear and hatred from everypony just as Tirek did their magic, Sombra would be much more powerful than him. And that's not even putting into account their abilities!

Sure Tirek has strong magic lasers, but Sombra can summon dark crystal constructions. Change his physical make up, and delve into the mind of others to use their fears against them. Tirek is out matched and out classed. Simple as that.