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As 6.2 CE won't get any more updates, I'd go with the newer series. Especially if you're selling stuff, you probably want to be on a version where issues (especially security issues) are fixed

At the risk of making an most unpopular comment, I would say  ... maybe Liferay isn't what you need for this one? I suppose that it all depends on what you man by "small shop" and what kind of services/integrations you are looking for. I am a Liferay Zealot from the moment I wake up to pretty much the moment I close my eyes, but there have been occasions where I have proposed different solutions for a handful of clients when I felt that Liferay might be overkill for their projects. It's rare mind you -- but in this case, this hits a little closer to home.

My wife has done "small to midsize" shop setup and consulting for a number of people now. Now I put the "small" in quotes because it all depends really on what you consider small. In her case though she has used a handful of platforms that specialize in ecommerce such as Shopify. Many of her clients have multiple properties and thy haven't necessarily migrated EVERYTHING over to shopify but rather provided a back and forth bridge between the two. 

Now I have to admit that I have not done much with Liferay Commerce other than kick the tires on it. I think it looks really good, and I like it -- but I am also intimately familiar with Liferay, the mantra, OSGI and how it all comes together. 

So again .. I suppose it all depends on what you mean by a "small shop" and what kind of integrations you are looking for. The shop aside, you should definitely update to the latest version of Portal because of all the reasons that Olaf gives and also all the awesome new features that have been released.