Capturing the Glib when i am an era behind in tech
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That's always pretty cool. I intentionally did that gambit one game even though I could have kept pace in research. Playing as Spain without horses, which led to a total bloodbath of a battle to take a Great Library City on a Hill (+100% defense with fortified units). Had a stack of 100 Medieval Infantry and Musketmen, and 50 Galleys to transport them (no Astronomy, of course!). They had Riflemen defending IIRC. Of course, all my Med Inf's were stuck with no upgrades when I did take the GLIB, as they didn't have Replaceable Parts (they got it a couple turns later). Still, a very fun gambit to do, even if it was counterproductive.
Of the options, obtaining the key resource is probably my top choice most often, especially when it's a real battle to get it. Generally any triumph when victory is legitimately doubtful is an ideal Civ moment.
To that end, my first Emperor victory is amongst my most fun Civ games ever, due to the triumph factor. Playing as France, I literally lost half my empire including all my core cities to the Americans when they declared war on me while I was fighting the Maya (I was sandwiched between them). I got lucky with leaders when I really needed some, and lost three entire armies of Cavalry turning the tide. I didn't end up gaining any territory in the war, and a couple of my cities were razed in the process (some by America, at least one by me intentionally to keep them from taking it), but I can't recall having a more come-from-behind victory. Even after that, it was very possible that the situation might repeat, and with lesser luck I might fall, but I was eventually able to gain the upper hand and avoid the devastating late loss that had befallen me in my previous Emperor attempt.
So my vost must go to "triumphal come-from-behind victory".