-Control of product listing and pricing
-Amazon customers are still offered Prime shipping
-Amazon handles all customer service, returns, etc.
-Ease of making changes to item information
-Higher Margins with no additional discounts or fees such as marketing co-ops and damage allowances
-Payments settled every 2 weeks vs Net 90 payment terms for most Vendor accounts
-Sponsored Product advertising and other marketing programs available only to Sellers
-Much faster response time from Seller Central "Contact Us" vs Vendor Central when problems or questions arise
There are also many resources that are only offered to Vendors including Amazon Vine, Subscribe & Save and other marketing services, and additional reporting capabilities with Vendor Analytics. As your brand grows and becomes more established, you may find value in a Vendor relationship to take advantage of these marketing programs.
There is a great feed in the Amazon Seller Discussion Forum that has lots of varying opinions and reasons why to choose Seller Central or Vendor Central. Read here.