I have been to Hagia Sophia, Notre Dame and La Sagrada Familia, so I was wondering what the most famous church in San Francisco is ?
You have named some of the finest such buildings in the world. San Francisco has some attractive religious institutions to be sure, but nothing I would consider truly world class or on the same scale as a church that has been under construction for 134 years.
That said, here are a few sights of interest though (inspired partially by this list, which has some others worth considering). I wouldn't really count any as a must-see for a tourist, but if you're interested in church architecture or want to visit one anyway, there are some good options. All these institutions have websites that list more detailed information, hours, scheduled services, contract details, etc...
Wikimedia Commons: Kjetil Ree
It has been featured in movies and has a beautiful interior as well.
Grace Cathedral Wikimedia Commons: Chris06
This is an Episcopal Cathedral, so I'm not sure if it is suitable for your religious needs, but it's a stunning building. One fun feature are the labyrinths, which are built for meditative walks. Come by Cable Car if you want to arrive in style, or the 1-California bus if you don't.
St. Dominic's Wikimedia Commons: Jdlrobson
Gothic-style Catholic church with a colorful and detailed interior.
Mission Dolores Wikimedia Commons: Robert A. Estremo
The namesake of the Mission District, this isn't quite as significant for the architecture but rather for the history: it is the oldest surviving structure in San Francisco and the site of the original Spanish Mission in San Francisco. It, along with the larger Basilica next door, continues to operate as a Catholic parish church.
(I couldn't find a free image suitable for embedding.) As you mentioned that you are Greek, it's fitting to include this one, though I've never visited. The interior decor looks quite striking. It is out on Brotherhood Way in the far Southwestern cover of the city, making it potentially a bit of a trip to reach depending on where you start.
Wikimedia Commons: Skier Dude
For something different, you could also consider one of the Bay Area's modern cathedrals. San Francisco's Cathedral (Saint Mary of the Assumption) may be mocked by some locals as the "washing machine church" or "Our Lady of Maytag," as it looks like an agitator from the sides (it is, of course, a cross from above), but it is a notable structure for better or for worse. Across the bay in Oakland, the Cathedral of Christ the Light is comparatively new and was the first cathedral built entirely in the 21st century, with lots of glass and natural light.
The Gothic-revival St. Patrick's church is nice and dates back to 1851. It is a far cry from the Sagrada Familia, but I mention it especially because it is quite convenient to Union Square, Muni Metro, and BART lines.
Also note Glide Memorial Church, part of the United Methodist Church, which isn't a whole lot to look at physically, but features an extraordinary gospel choir, plenty of spirit, a commitment to social justice, and prominent programs to feed and help the homeless (and they can always use more volunteers).
Some other architecturally significant buildings affiliated with some religion in San Francisco include: St. Ignatius Church, Calvary Presbyterian Church, Old St. Mary's, Tin How Temple (Buddhist), Hua Zang Si Temple (Buddhist), Vedanta Old Temple (Hindu), Temple Emanu-el (Jewish), Sherith Israel (Jewish), and Beth Sholom (Jewish, modernist). I have surely omitted others from this list.
To use a decent empirical measure of popularity, Grace Cathedral is the highest-rated church in San Francisco on TripAdvisor, with 700 reviews averaging well over four stars.
Grace Cathedral is an Episcopal cathedral on Nob Hill, San Francisco, California. It is the cathedral church of the Episcopal Diocese of California.
The cathedral is famed for its mosaics by Jan Henryk De Rosen, a replica of Ghiberti's Gates of Paradise, two labyrinths, varied stained glass windows, Keith Haring AIDS Chapel altarpiece, and medieval and contemporary furnishings, as well as its forty-four bell carillon, three organs, and choirs.
Here's a link to it on Google Maps, where you can find its location in the city and get directions.
I will post what I eventually did, since I believe that the route one follows to go these churches plays a significant role too, and most importantly, a personalized description is always useful!
I will upload my pictures in Travel:USA | G. Samaras.
So, could I guy like me be impressed by a church in SF? Hell yeah! How?
Cathedral Saint Mary of the Assumption
That's something unique for me.
So here is the plan we followed (Note: We went by foot, it took several hours) on Google Maps, παραμονή της Παναγίας, 14 Aug 2016, Sunday:
Saints Peter and Paul Church: My brother chose that one, because Saint Paul is his favorite church in Greece. It had a liturgy by the time we arrived. Nice church, 2/5 of the church was full of people attending the liturgy and the priest asked who was a tourists (<2/5, including us).
Except from the priest, who had a chair to sit (!), there was a person narrating from some holy book I guess, another one (the chanter) and a woman, who would bring the corresponding book to the priest at some times.
The church had nice colored windows and a nice room for prays, were you could light up your candles for 5$ each. There was a person that seemed to be making sure everything is ok with the candles.
Huge drawback for me, was the fact that it had music (as all(?) the Catholic churches I guess), which for an Orthodox Christian like me, was very irritating and unpleasant, it didn't allow me to feel what I wanted, to be honest, but that's including when exploring!
Remarkable advantage for me, was the fact that the neighborhood (and the route I followed as indicated on the map) was a beauty, on a sunny day. The church lies just around Washington Park, which had many people, and some event was taking place (there was live music). Moreover, the Italian Restaurants nearby seems elegant, but I wasn't hungry at that time.
This church seem to be the less touristic from the other two.
Grace Cathedral: That church is the baby of the Notre Dame in Paris, at least through my eyes. It is too touristic inside, but it must be bigger than the church we visited before.
It had too beautiful colored windows, and music playing, but it was live. In fact there was only one woman who played the piano (or whatever this is called, I remember an algorithm in Multimedia to be named after that organ), and there was no liturgy at that time.
The tourists were able to go (almost) everywhere inside the church (which was not the case with the previous church), something that really doesn't characterize a church, but it allows you to see everything from a close view.
I lit 5 candles at that church, there wasn't a fixed price for them.
Cathedral of Saint Mary of the Assumption: Its terrace is so stunning, simply amazing, modern and unique for me!
It must be a tourist attraction, since buses with Asians had surrounded the place, disembarking people ready to shoot with their cameras! :)
It is big, but it's not only the building itself. It has parking spaces and the "corridors" to the door were long (like bridges), in opposition with most of the others churches we had steps that would guide you to the door directly. Here, there were some steps, then you had to cross that "bridge" and then find yourself in the door.
Unfortunately, tourists were not allowed at that time, since two βαφτήσια were scheduled, but I was able to take a glance from the window, the roof follows the shape of the terrace and it seemed like something beautiful was at the end of the room (diametrically from the entrance), but I am not sure what.
There was a park nearby, just before a baseball pitch, but there wasn't any event there, just <10 people laying on the fake-plastic grass (something that most of the parks have here, unfortunately).
The route we followed had some nice places, which a person that has gone places, should pinpoint easily, given that he has his eyes open. Many other churches were found around, with a Chinese one, being the most distinctive, it was a building like a big house, with a triangle as a terrace.