It's a great question, and one your doing well to ask before you spend a lot of time and money on content.
100% any content you produce should go on YOUR site. Content takes time, and if done properly is a huge asset to your website in terms of equity with Google, and long term traffic.
Imagine you have a business reconditioning Rolex watches (for example). You write a fantastic article about the history of Rolex, slightly signposting your own services. The article goes good-guns, trends socially and starts generating traffic. Now imagine two scenarios;
1. You published the article on your website
2. You published it on blogspot.com
Scenario 1
The users come, read the article, and generally find it informative. Because you have an attractive, well structured website with good calls to action, some of the users click your ENQUIRY button, and contact you regarding your services.
RESULT!
Scenario 2
As above, users come, read the article, and generally find it informative. However, the website they are on is blogger.com. It doesn't seem to be a website offering any product, or any services....its just someones blog. There may be a link which can offer to take the user to your website....but that doesn't look anything like the site which contained the article they enjoyed reading. Your gonna have an up-hill struggle trying to convert visitors on blogger.com into sales on yourwebsite.com
In terms of buying articles; It really depends on what the focus is; Are you looking for content to push out socially? Content to improve your websites? Or content to target new traffic organically on Google? If it's Google traffic you are looking for, then your content needs to target specific traffic/keywords, and the writer will needs skills aside from just being good at writing.
Have a thinking about a content strategy, or engage with an agency/freelancer who can help you with a content strategy.
Best of luck.