It is always difficult to select a service suitable for online business. If you are a startup, your whole business might depend on external website. Same is the case with selecting website screenshot provider. I had difficult time selecting one. There are some good service provider but they are expensive, and cheaper ones might not live upto the expectation. In the past I did a small comparison of price and services and my winner which ultimately turned out to be my personal favourit is http://www.w3snapshot.com. Reason for selecting this tool for generating website thumbnails was performance, reliability and price. w3snapshot works on credit, you just need to buy credit and you can use services as long as you have credits. No monthly fees or any thing like this.