Never utilize a free domain/subdomain. Purchasing your own domain name is not being pricey and puts forth to your upcoming visitors that you are significant enough about your business to speculate in a good relevent web site name. Not only that, many search sites will not efficiently index free domains, and many promoting sites hate to see sub domains so you will not be able to use there services.
Your domain is your window to the Web and should reflect the type of business you are building or the niche that you've decided to channel your attempts. Having a domain such as bobsbusiness.com is not a good name unless you are marketing BOB. It should reflect your business and should have relevance to your product.
There are a lot of tracking and statistical data sites that are also negative toward domains that you do not own. In several cases to prove you own the domain you will have to upload a file to the root index of you site as a security measure to make certain you own the domain and not just trying to get information on a domain you do not own. Only by owning a domain that's hosted by a proper internet host will you have access to the root index.
Spending those few dollars on your domain will also guarantee you don't waste good marketing efforts too. You start a site on a free host with a free sub domain and for some unknown reason you site begins to take off. Now what? You have got to now get your own domain and hosting and this may totally screw up your selling links back to your internet site and now you are back to square one.
If you are going to build an online business... Spend the few dollars on your own domain and a reasonable hosting provider. Google will love you, your clients will have more trust in you and your advertising efforts won't be wasted.