Generally, video cards rolls off of the production line from the same OEM (original equipment manufacturer), then a brandname sticker is slapped on whether it is Asus, Sparkle or XFX. Sometime a brandname like Asus or Palit decides on a custom design specific for their own brand (I'm not talking about a mere change of the heatsink), but are usually restricted to higher end models.
The parent company of Sapphire is an OEM who manufactures ATI cards for most other brands.
There is no quality difference between Sparkle and XFX. XFX generally has a better reputation because they have been in business of selling video cards longer than Sparkle. Also, their higher end cards comes with "Double Warranty" meaning the warranty will transfer from the original owner to someone who is looking to buy it second hand. The warranty only transfer once so if it is sold to or given to a 3rd owner, then the card is no longer under warranty.
If Sparkle is the same company I am thinking about, then they have expanded from power supplies into video cards.