I think it's a bit the services - I am very impressed with Aurora on AWS for instance, and there isn't really anything equivalent to it anywhere else. Also, some of the services elsewhere seem easier to deploy or more convenient to use.
In any case, all three big ones are pretty good for almost anything, and I don't think there is anything that's doable on one that's impossible to do in the others (IBM is the exception here - if you need AIX, IBMi or Z, they are the only ones who can offer that).
In any case, all three big ones are pretty good for almost anything, and I don't think there is anything that's doable on one that's impossible to do in the others (IBM is the exception here - if you need AIX, IBMi or Z, they are the only ones who can offer that).