Barcelona or Madrid or San Sebastián?

Been watching YouTube videos and we are no closer to making a decision about where to visit/live or a few months. San Sebastián seems a bit small to me as I enjoy large cities for all the amenities but seems beautiful and seems to have a good food scene. Barcelona seems huge. I have a friend who just got back from Madrid and he loved the food (said it was some of the best he’s had in Europe). Currently, I live in a larger US city, that is hot and humid. Ideally, I want a bit of respite from heat, at least some seasons. I think I desire a bit of an expat community as I am not naturally gregarious yet like to hang at pubs and play board games and DnD. I am also mostly on a plantbased/vegan diet.

So which city might be best for a vegan boardgamer?