surely it would make sense to use them both ?
Have you read up on the use of metatags ? it may be best to read a little about them to understand how best to use them within your store. There are varying opinions on what actual effect they have on overall SEO, for a while there Google were not placing as much inportance on them as previously, when people started to keyword stuff their meta information,
Google are now slowly bringing them back into play within their algorithms, so a little research into keyword stuffing and what it means would be good before you start on them ,
Best to make an informed decision first off after a little research than to find out, as many do that the original meta data entered in a rush doesn't have the effect they think it should with their rankings and search engine placement.
Google if you go to it and pay attention to how you ask it to find things and the responses you get to the typed search query, will now really become your friend as you google to find the information I've suggested above ....... when you find a relative piece of information ...remember what you typed to get that link as a result ??
Does that make sense ?
Keyword research should be a part of your store set up from the word go so as to give yourself the maximum chance of actually ranking the store or site you are building, and reaching your intended target market, rather than to find you need to re-jig and refocus and in some cases re-write parts of your site, after a few months of not getting the audience you were wanting,
The success is in the planning, wether you are a diy site builder or pay £1000's for the design and build of a site, the lack of planning will determine your success rather than the money spent on a designer, to start off with what you would like your business to achieve and what it is going to take to get it there, read, learn , ask questions and seek advice, work out a plan

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