If your goal is rankings, you definitely need to create unique content on your website - not just slightly different, but completely different. Larger retailers will tend to outrank you simply because they have enough brand value that their SEO is inherently better, even when their content is not as good. Smaller businesses can outrank by optimizing for longer-tail keywords and by adding unique content and value to their sites. Be sure that if you go to this trouble of creating unique content, you also periodically check the retailers' websites and make sure they are not copying the descriptions from your site.
In addition to the products themselves, I've had good success with creating related value-added content. For example, I used to sell scooter accessories, and I personally found it hard to locate dealerships. So I did a lot of Googling and made a scooter dealership directory, complete with filters for what brands each one sold. I got a ton of relevant traffic from that - people who were interested in buying or servicing their scooters - and that did more for my SEO than all the product copy optimization I could have done.