1) Zeus - Must have GB for anyone who ever does any kind of fighting. Even if it's just couple of map fights occasionally, it is already then worth it. It costs almost nothing goods wise and it is 6 tiles size, almost 3x smaller than any other GB, so having it has very little downside at all.
2) Babel Tower - Having 1 doesn't really hurt you if it's on high level, because of the goods it makes, but the benafit is so minor it is not worth the trouble and time it takes of getting it leveled. But in my PE town, I would prolly take one lvl10 Babel if I could get it like that.
3) Lighthouse - Must have GB for everyone.
4) Colosseum - GBs were released when I was already in CA and by CA that happiness output is sub-par already. Even on lvl10, I would have razed it if not when I got Trading companies in CA, then for sure when getting Water Pumps in InA. I think it's like 95 per tile on lvl10. TC is 75 and 150 polished, WP is 85 and 170 polished.
5) Hagia - Again happiness. Happiness GBs are smth that get outdated. Benafit was too minor, so didn't get one. I think it was like 140 per tile on lvl10, so polished water pump starts beating it. It has a nice 2ndary bonus tho in FPs. Good enough to make me at least consider building it. But decided too much trouble, some extra FPs are not that huge if u are at end of research trees 99% of the time
6) Cat of Aachen - Must have GB for hardcore PvPers.
7) St Marks - Must have GB for everyone.
8) Notre Dame - similar to Hagia, but with no useful 2ndary bonus. Most people around that stage choose to build either one or the another. And it is usually Hagia cause it can be get first and gives FPs. Leaving Notrde Dame problaby the least popular GB in the entire game, meaning it is hardest GB to level up as most ppl are ust not ineterested in it. I would have taken it at lvl10 in CA or InA, but razed it in PE. So I didn't go through the trouble of getting it and then getting it leveled knowing soon I will raze it anyways. And like with all happiness GBs, b4 it actually gets to that high lvls it's wasteful, and if takes a while..not good, didn't bother with it. But I considered it in CA yes.
9) Basil - Defense GBs are waste of space for me, they don't really help me make more points. Getting plundered is not really an issue for me and even if it were, defense bonuses won't stop hardcore PvPers from coming through. I think I have addressed quite long in another post why defense GBs are so underpowered compared to offensive GBs. I won't do it again here, so u can just take my word for it
10) del Monte - Must have GB for PvPers, prolly the first offensive GB you want to build if you plan to go for all 3 because of the best 2ndary bonus. Highly recommended for even casual fighters because of the great 2ndary bonus(FPs)
11) Dresden Frau - Very underappreaciated GB. Goods is actually a brilliant 2nd bonus which does not age. I built it during CA and my math told it me it's gonna be good in InA, PE and even the age that comes after it. And because goods buildings got so large, it's prolly gonna be worth itself till end of time. Nearly 200 happiness per tile that takes no polish and enough goods per day that 70% of a goods factory makes. Add the 2x2 road reqs in PE, the thousands of population goods factory takes, all the culturals that population takes, and u get that Dresden is much better at producing goods than ur actual goods factory in PE. Oh and it also gives 5k happiness as bonus
12) Deal Castle - it's large, but if u need medals, u can live with it. I had one on lvl10, but razed it reciently. For me that 3k medals per month was no longer big enough number to be worth those 49 tiles just because I have won all the medal expansions and even if we get new ones next age that's gonna cost 20k and 25k medals each, I will have enough medals stock to get em asap. Besides I could make much more from quests than from Deal castle by now. Also gives defense bonus, what can be a boost for some players, keep away some oppurtunists in ur hood perhaps.
13) Capitol - Difficult to decide for sure, it has many different sides. Currently the only real strategy where Capitol is for sure worth itself and great, is if you built 90 kings during the summer event. With other stuff, it is so and so. U can make some minor points profit with it by getting some more supplies. But that comes at the cost of having very one-diamentional collect(almost no coins, way too many supplies). there might come different startegies in future though where Capitol will be great, I can already think of what they can be like. Right now it might be worth also for some ppl really struggling with space and population to get military and who really don't care about how much coins or whatever they collect.
14) RAH - Very very highly recommended to have GB for everyone.
15) Frontac - Unless u go for medal rank and do lots of rotating quests per day for it, I don't see any reason why have 1 in ur town.
16) Alcatraz - Looks great for everyone who ever does some fighting. With PE large military buildings which take so much 'footprint' size when u count the population, culturals and everything, it's already worth itself in very first levels, even if u lose all those unattached units u make every day. But usually u won't let em all die anyways, since u remove out the unhealthy ones. Next day they will be also healed, so slowly u will get a huge stock of extra units with it.