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I've currently got active accounts with all three of those VPS providers - I love them, and use them every day - particularly Linode, but also Slicehost/Rackspace, and DigitalOcean. I even have a bare metal server at ServerBeach - which I realize I need to shut down...
At this exact instant I have six terminal windows open across DO/Linode. I host a moderately popular California Food Blog, and have about 15 years experience in various companies that have had hosting responsibilities.
I'm not saying you can't do great things with the VPS providers - I'm just suggesting that the tradeoff between saving $2-$3k (at most) with Digital Ocean, would be more than made up by the technology risk, hassle of having to re-invent a lot of the services that you get automatically from AWS.
That could change sometime in the (near) future - but right now, AWS is an easy (and honestly, all things considered, relatively cheap) solution for this type of application.