I would personally suggest setting up your company in a jurisdiction with a territorial based tax regime. Hong Kong companies are subject only to profits tax on income arising in or derived from Hong Kong itself. If most of your customers live outside Hong Kong, full tax exemption could be reached. Note however that both Argentina and the USA tax on a worldwide income base. If you already have an Argentinean or USA based company, this could lead to taxes being levied on the income from the internet business in one of those countries. Argentina is negotiating a double taxation treaty with Hong Kong (the USA is not), but it has not been concluded yet. To mitigate or exclude the risk of double taxation, it could be suggested to set up a second holding company which is situated in a jurisdiction with double taxation treaties in force with both the USA, Argentina and Hong Kong (such as The Netherlands, Austria, Belgium and others). Do consider however that much will also depend on the type of E-commerce conducted, is it a fully internet based business or are physical goods sold and delivered by the company etc. If you would like, I can suggest a consulting firm which specializes in setting up tax structures for Internet based companies and has a wide expertise in International Taxation, if you would like to have a more detailed advice.

When you say you are an American, I assume that means you are a US citizen, which means you are subject to tax on your worldwide earnings. Since all of your business is generated from outside the US, you probably do qualify for a foreign earned income exclusion and you may be able to incorporate the business as a C corp or similar structure, in a tax favorable country to defer US income tax, but at some point when the business earnings pass to you as an individual, those earnings are going to be subject to US tax reporting.

If you are not a US citizen, then you have a lot more flexibility in structuring your business to avoid US taxation.