Both parties are described as (Irish) nationalist by Wikipedia. After losing all Westminster seats in 2017, the SDLP made a comeback this December, gaining back two seats.
Speaking of seats, unlike Sinn Féin, SDLP seems to take their seats at Westminster; in fact the current SDLP leader even criticized Sinn Féin for not doing so. Also, Financial Times recently described the SDLP as "moderate nationalists". But how does the SDLP nationalist position otherwise differ from that of Sinn Féin when it comes to the path they see for Irish reunification?