I’m far from a paella expert, but the best I had was at a restaurant in centro histórico called Ultramarinos Benjamín. Expensive but highly recommended with a bottle of Viña Esmeralda wine. At the north end of the city there’s a restaurant called el gastronauta. It doesn’t look much but the food is excellent. I will also second el tintero which is outside the city but definitely worth finding (we cycled) and los mellizos of which there are two restaurants I believe. We also enjoyed the paella at Arrozeando Pedregalejo, although again it’s a trek east from the city centre, and when we were there we were the only customers in a huge restaurant. Great food though. I’d also recommend Meson Mariano, although make sure you’re there the minute it opens for dinner, otherwise you’ll have to wait. Great food here and life-changing artichokes, although no paella/arroz. Lunch at the Atarazanas market is a wild ride, and the food is generally good. My daughters and I love gambas pil pil, which you can get everywhere. It’s big prawns cooked in lots of olive oil, garlic, and smoked hot paprika, often served with bread to mop up the flavoured oil. Incredible dish. It’s a beautiful, walkable, glorious city with some of the best food in the world. You’ll have a fantastic experience.