1. Go for the Throat / Cast Down / Ultimate Price
The power level of all three of these is exactly the same, and their flexibility is highly dependent on the contents of the cube. Usually, Go for the Throat ends up being the most powerful one, because there's typically less must remove artifact creatures than there are legendary and multicolor ones. Cast Down and Ultimate Price are often comparable, though this, of course, depends a lot on the themes one runs in their cube. Let's have a look at the creatures in your Highball cube that you would want to kill but can't touch with each spell.
Go for the Throat (8): Combustible Gearhulk, Metallic Mimic, Steel Overseer, Porcelain Legionnaire, Scrap Trawler, Hollow One, Scuttling Doom Engine, Walking Ballista
Cast Down (15): Anafenza, Thalia, Sai, Zahid, Yawgmoth, Tasigur, Kari Zev, Alesha, Pia Nalaar, Pia and Kiran Nalaar, Polukranos, Ghalta, Teysa Karlov, Roalesk, Sidisi.
Ultimate Price (14.33): Senate Guildmage, Soulherder, Psychatog, Hostage Taker, Bloodhall Priest, Knight of Autumn (in 4/3 mode), Pitiless Pontiff, Teysa Karlov, Deathrite Shaman, Underrealm Lich, Roalesk, Boros Challenger, Butcher of the Hoard, Sidisi, Siege Rhino.
Heh... Spot on
Note that I prefer Cast Down or Ultimate Price, precisely because there's a few more untouchable targets in the cube, but also because those targets are spread out across decks, whereas the must kill artifact creatures often end up in one or two decks, making the card a god tier kill spell against half the table, and decidedly more mediocre against one or two opponents. I don't like the variable effectiveness in that, for much of the same reasons that I don't like "protection from (color)" on creatures in draft.
4. Smother
I think this is a noticeable step down from the previous three. Still gets a lot of targets, but not at a great rate (on average you will spend 2 mana to kill something that's 2 mana). More importantly, it can't ever hit the most impactful targets on board. I prefer something like
Disfigure or
Last Gasp in the "kill small creatures" slot, since those can at least target high cmc creatures.
99. Murderous Complexion
This is just a bad card. Has a really, really hard time killing utility creatures, can't kill a blocker, and unless you have a discard outlet, you will take one painful hit before you can even use it.