Well it depends highly on your skill to install the software (no offense i just don't know where you are coming from) and the predicted growth of the shopping cart.
let's say you are selling stickers for an upcoming community soccer tournament on your blog, i would suggest you just create pages and paste the Paypal code(or whatever gateway you use)
now if your store is going to have a longer life and will grow to a small business , i suggest using a dedicated software, there are some good options both opensource and SaaS, Shopify seems good, PrestaShop is also proven, there is also a e-commerce extension for wordpress.
I lean toward OpenCart (opencart.com) it's a great turnkey solution, simple install, comes with plenty of gateways and shipping methods and i've used it in several small stores with great sucess.