Simply check out their fees and charges. They'll all typically have a single fee per month for usage and then other transaction fees such as 30c + 5% of every transaction value.They're all very similar in this regard.
Then it's just a case of ensuring that the website is easy to manage and it's quick to maintain products etc. Half the battle is having the confidence to work on the site and get your hands dirty. Having the best looking online store in town is great but if it's at the detriment of ease-of-use then it's no good because things will quickly look out of date on your site because you're not getting there.
From experience it's important to feel like you have the confidence to use it. If not then you'll think twice about adding new products, adding new images, changing prices and stock levels etc. All of which you WILL need to do and is important.
I like
Squarespace and
Shopify.