Tbh both are pretty good I’d say a brand working with an artist is slightly better though because magazines are usually not going to have the same person on the cover often but if a brand is wanting to work with you they could possibly have you represent them in multiple different magazines. An example I can think of since it’s so recent is hanbin’s Swarovski think was done with Elle but it was arranged by the brand and it was the brand who selected him which is why his shoot is not only on the Elle page but on other magazine instagram pages too. Outside of magazine shoots I think a brand showing that they want to personally contact and work with you for something shows that your wanted in the industry too and can help you build a strong connection with that brand and might even make others interested in you.