I would probably say Weapons, Sinners was really good too.
Is still have to see The Long Walk, Companion and Good Boy. Btw The Long Walk's concept is taken from an older sci-fi b-movie from the early 2000s. I will have to post about it.
I don't know if it's the best, but I liked that 28 Years Later wasn't a typical sequel, the ending almost reminded me of Six String Samurai and there were other points in the film that seemed to suggest a subtle black comedy approach.