I think Google will treat both situations roughly the same. However, your own domain will give you more control.
Long answer: When you don't have your own domain you'll have the .subdomain name in it which isn't 100% keyword friendly. For instance. My site at Sell Your Mobile has 100% of the keywords in the domain name and not sellyourmobile.blogspot.com. However..... That doesnt matter if you have enough backlinks with your anchor text as you want it. Many blogs with the .blogspot or .wordpress subdomain can get just as much search engine traffic as a site that has its own domain name. Also bare in mind buying your own domain name is fine and all but unless you actually own the site where your sites files are hosted and they decide to pull the plug on you all your content is gone. (Unless you save it) So it's good to have your own domain name. But if it's a serious site you should have and own your own hosting account to host your site too. (Just in case) Short answer: Yes but there's more to it than that. (See above). Hope this helps. Rep if so