MSI and Sapphire are manufactures that make and sell ATI Video cards. ATI designs and makes the GPUs and then they have AIB partners that actually build the boards and sell them. So a Sapphire radeon is an ATI card. This is actually how pretty much all of the video cards are done now.
The particular AIB partners just generally do different cooling solutions or overclocking and things like that. Sapphire is a good one, MSI is OK, but better with Motherboards. XFX is really good as well, and has some great warranty support.