This a copycat thread since Tephros' Unique Unit poll seemed to generate a nice discussion. There are so many factors to consider and different approaches to this game that a poll of unique buildings is probably meaningless, but we're just here to have fun anyway. Just pick your favorite.
Like Tephros, I had to exclude 9 options because 25 is the maximum number for the poll. That wasn't an easy task, but the ones I chose and my reasoning are below:
Shale Plant (Japan), Assembly Plant (Germany), Mall (America), and Research Institute (Russia) are out simply because they come so late, so there's nothing special to help you out for the vast majority of the game. They all have nice bonuses when you finally do get them, though.
Stele (Ethiopia), Salon (France), and Pavilion (China) are mostly just useful for cultural victory and provide no additional benefits other than culture, so they're out. (Hey, I had to narrow down the list somehow. These are good in specific situations, but UBs that provide other benefits are more versatile.)
Totem Pole (Native America). Wish I could have left this one in, because we all love extra exp, but it's still a pretty limited UB that becomes obsolete halfway through the game.
Dun (Celtia). This one's obvious.
Just to make things a little simpler, let's assume we all play without unrestricted leaders, so for example, don't pick the Roman Forum because you like it with Philosophical leaders. I think that synergy with a leader's traits is an important consideration in determining the quality and usefulness of a unique building.
My favorite UB, by the way, is the Ikhanda. It comes from the very beginning and lasts the whole game, it's cheap with Shaka's Aggressive trait, and -20% maintenance means 5 cities for the price of 4, 8 for the price of 10, etc. It really helps make Shaka a beast in the early game and keeps helping all the way to your inevitable domination victory.
Like Tephros, I had to exclude 9 options because 25 is the maximum number for the poll. That wasn't an easy task, but the ones I chose and my reasoning are below:
Spoiler :
Shale Plant (Japan), Assembly Plant (Germany), Mall (America), and Research Institute (Russia) are out simply because they come so late, so there's nothing special to help you out for the vast majority of the game. They all have nice bonuses when you finally do get them, though.
Stele (Ethiopia), Salon (France), and Pavilion (China) are mostly just useful for cultural victory and provide no additional benefits other than culture, so they're out. (Hey, I had to narrow down the list somehow. These are good in specific situations, but UBs that provide other benefits are more versatile.)
Totem Pole (Native America). Wish I could have left this one in, because we all love extra exp, but it's still a pretty limited UB that becomes obsolete halfway through the game.
Dun (Celtia). This one's obvious.
Just to make things a little simpler, let's assume we all play without unrestricted leaders, so for example, don't pick the Roman Forum because you like it with Philosophical leaders. I think that synergy with a leader's traits is an important consideration in determining the quality and usefulness of a unique building.
My favorite UB, by the way, is the Ikhanda. It comes from the very beginning and lasts the whole game, it's cheap with Shaka's Aggressive trait, and -20% maintenance means 5 cities for the price of 4, 8 for the price of 10, etc. It really helps make Shaka a beast in the early game and keeps helping all the way to your inevitable domination victory.