In the "CC? Why bother?" deck thread, it was discussed whether or not Steam Machine could be used to supplement or replace the Lava Destroyers. Some quick math revealed why the LDs were still the better choice, but I felt like it was a bit too statistical. I wanted a cleaner one-line explanation. And they say a picture is worth a thousand words, so.....
Let's track the attack strength of Lava Golems, Lava Destroyers and Steam Machines over 20 rounds:
As expected, the Steam Machine becomes stronger than the Golem after four rounds, and stronger than the Destroyer after 6 rounds.
But that's not the whole story; let's compare the
total amount of damage done by each creature over the same 20 rounds:
Now this is much more interesting. Even though the Steam Machine becomes stronger faster, it will still have done less damage than the Lava Golem would have until the 9th round! It doesn't pass the Lava Destroyer in damage potential until the 13th round!
What if we compare how much quanta you spend to how much damage you get?
Sadly, at no point is the Steam Machine ever the best option for damage per quanta spent.
It's worth keeping in mind that the round numbers above aren't from the start of the game; they're from the round when the creature is first summoned. And they assume that you'll be able to buff every creature every round. So in order for the Steam Machine to be useful, you have to get it out early enough for it to attack in at least 9 rounds, it has to not be rewound or mutated or frozen or delayed, and you have to be able to pay
for each of those 9 rounds.
TLDR: You're probably better off with the Lava Destroyer.
(I can use this spreadsheet to analyze other buff-able creatures, if anyone wants a comparison for their own decks. I'd also like to extend this to figure out the effects of things like Fire Bucklers and Thorn Carapaces, to determine when the Steam Machine's extra health makes it a better option. Not sure how to best accomplish that yet.)
Edit: Tweaked numbers for accuracy.