I am going to run few eshops as I have already finished my work on them.
I assume pacifichost.com can be a good option for me as they allow to host unlimited domains within one hosting account and can be good for running eshops.
Do you think that OS Commerce can be a good for me? Or it would be better to choose Zen cart or Cube cart?

I can say that OS Commerce can be good software for running ecommerce web sites, but you should be confident that the company you are going to deal with is reliable and trustworthy.
I know nice ecommerce hosting opportunities could be got from webhostingbuzz.com as their cheap hosting plans are optimized for running e-shops fast and efficiently.

I believe you need to find web application first and then start thinking about web hosting

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Exactly. that's a good point. find a web app that you need, install on local computer, test, configure and then look for the web host that will meet the needs of the particular app. for example weather you need a .net host or linux etc.

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Moreover, on the official web site for certain web application you might find a list of suggested web hosts.

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Good point. Didn't think about that.

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Think that OS Commerce shopping cart software is a perfect choice for running e-shops but still can recommend you not to be so confident in choosing web host as there are many options to look at. Say marblehost.com offers nice shared hosting plans along with Os commerce included to them. I would better choose them if I were you.

OS Commerce shopping cart software is a perfect

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I think joomla + virtue mart plugin is easier to use.

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OScommerce is ok but there are much more robust platforms available. X cart and Interspire are 2 of my favorites. Virtuemart is also a great OS program

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