It also depend on what requirements your business has and who you have available. The skillets are different and they overlap in places, but one way or the other if your business is growing your operations requirements will grow.

I am hugely in favour of AWS for web startups I am involved with because 1) I know AWS very well, 2) they provide hundreds of thousands of euros/dollars of credit to startups (I think all the big cloud vendors do at this stage), 3) it's useful to have architectural flexibility, and 4) they can take on a bunch of the security and availability burden that can otherwise be very labour intensive in a small company.

Also you can pry S3 and RDS Aurora out of my cold dead hands!