Grammy Award winners Smith and Williams will face off for the Favorite Male Singer prize, alongside Justin Timberlake, Nick Jonas, Bruno Mars and Blake Shelton, while Swift and Beyonce join Ariana Grande, Selena Gomez, Nicki Minaj and Katy Perry for the female honour.
Favorite Music Group will be a battle between the likes of Coldplay, Maroon 5 and One Direction.
The stars up for Favorite New Artist, which was among the early categories announced on Thursday (19Feb15), include Five Seconds of Summer, Iggy Azalea and Meghan Trainor, while Favorite Song of the Year features Jessie J, Grande and Minaj's Bang Bang competing against Trainor's All About That Bass, Swift's Shake It Off, Azalea's Fancy, Perry's Dark Horse and Problem by Grande and Azalea.
Meanwhile, in the Hollywood categories, Guardians of the Galaxy, Maleficent and The Hunger Games: Mockingjay - Part 1 are among those shortlisted for Favorite Movie, while Angelina Jolie, Emma Stone, Hugh Jackman and Mark Wahlberg are all up for best movie acting accolades, and Meryl Streep (Into the Woods), Cameron Diaz (Annie) and Jolie (Maleficent) are in the running for Favorite Villain.
The winners will be announced on 28 March (15), when Nick Jonas will host the 28th annual awards show in California.