For Biz20, generally we would recommend for informational website.
For Biz40, generally we would recommend for new ecommerce site.
For VPS nowadays we will recommend only when client require customized set up.
From Biz20-Biz120, the difference is only storage and computing power. The more storage you have the more data you can hold. The more computing power the more visitors or processing it can do.
Why ecommerce sld go for Biz40 and why informational website can go for Biz20 is because ecommerce website by nature, there are more user interaction with the site, more activities to add data, more data are added in daily, and usually these means more computing power needed. Informational website is usually one time install, and for most times, the server only need to serve static files, which generally are not very heavy duty.
