At this point, I'd just be happy if Adele came back
But her album will probably dominate Frozen-style (with bigger sales) and Rihanna will probably dominate the singles chart. Of course they'll be a couple of new artists who rise up.
taylor is looking to be a top contender if 1989's sales keep being strong, blank space is showing really promising signs of being a future hit so i could see it giving her longevity at least until a little bit after the end of the year and subsequent singles might do well too
adele has a good chance too, we can't really be sure what her album will do
and i don't see any reason to think R8 will do any better than the average rihanna album, which means it'd do really well but not quite dominate the entire year you know