Different articles and sources give different numbers, so don't take this as gospel, but: IBM's *-as-a-service ARR is larger than Google Cloud's. Oracle claim

Different articles and sources give different numbers, so don't take this as gospel, but: IBM's *-as-a-service ARR is larger than Google Cloud's. Oracle claims theirs is too, but my understanding is that they roll a lot of their licensing costs into the same reporting, so it's hard to tell for sure.