Do I need reservations for most popular restaurants in Barcelona and Madrid?

I really appreciate all of the guidance here, you guys have been amazing. I (32 F) am going to Madrid and Barcelona for 7 days in February. I am looking for advice on if people generally make reservations for dinner.

Any favorite spots or dishes are also welcome. Thank you so much!

Side note: I’ve done hours of research and have lists of places but I need firsthand feedback!