I am glad you started this thread. its an interesting topic: (Spoilers for clannad follow, You have been warned)
Clannad for me is my favorite anime series of all time. It is my favorite anime in the romance genre too and that is simply because the different story arcs in it are truly beautiful and so amazingly pure. This anime is by far is one of the most realistic and one of the most purest ones that i ever saw when i first got into anime.
The reason for that is simply because i went into this anime blind meaning that i never knew that the series alone was based of adult games for the PC. I started this anime thinking OH MY GOD....this pacing is killing me and it wasn't until episode 7-11 that the story pace finally started to speed up a little bit and when it did the anime itself was truly magical.
I NEVER imagined that we would see the life of Tomoya Okazaki from his teenage years through to his adult life where he was married and had so many responsibilities. The anime itself taught me a lot and i now that it had the whole harem aspect to it. However the harem aspect was NEVER as over the top as SAO and that is what i think truly allowed it to flourish as a pure romance story.
I loved how there were little to no sex or sexual related stuff in it since that is what made it so damn pure. It is the type of romance that we will probably never see in the real world but regardless it was an amazing experience seeing what Tomoya went through. How he met this girl who had her illness and how he ended up marrying said girl and then even having a child with her and this ofcourse led to tomoya having lots of responsibilities as an adult as well as the fact that he had to overcome so many hardships during the course of the anime.
I truly do recommend this anime to ANY anime fan who loves romance. It definitely wont let you down if your one who can appreciate beauty or if you have a kind heart. The anime has two seasons and then there was the movie which served as a great epilogue.
OMG even as im writing about this anime, i am getting flashbacks and so much nostalgia from events that occurred within the anime.
My favorite quote from the anime itself would be:
"I hate this town. It's too filled with memories I'd rather forget. I go to school every day, hang out with my friends, and then I go home. There's no place I'd rather not go ever again. I wonder if anything will ever change? Will that day ever come?"
~ Narration by Tomoya Okazaki
When i first heard this quote, it really resonated with me since it really reminded me of how i felt about my current town and how i myself wanted to escape the drama of life and just settle down somewhere quite.
Well that is the end of my ballad on why Clannad is my favorite anime.