ATI make the chips for all of the cards and provide reference designs for
those cards made by the other companies (normally referred to as OEMs -
although there are other terms too) - these are the makers of "Powered by
ATI" cards. Some OEMs introduce features or functions not seen in the "Made
by ATI" products. A good example of this is Sapphire's "Ultimate" range of
high end cards which use passive cooling through very large heat sinks
whereas the "Made by ATI" cards with the same chips use chip coolers with
fans.
Which brand you buy may be dictated to an extent by where you live/what
country you buy in. An example of this is that these days ATI only
distributes its retail product range to North America and Canada so outside
of these areas it may be hard sourcing genuine Made by ATI retail packaged
products. Just to confuse things, ATI also make products themselves just for
OEM markets, these may be distributed through different channels to the
retail products. An example is that here in the UK we'll soon be seeing the
OEM but "Made by ATI" eHome Wonder become more widely available (although
it's already around here if you look hard enough). Pesonally I don't like
the fact that retail made by ATI products aren't sold here anymore (they
used to be) because its one less player in a competitive market but then you
could always buy the product over the web from a US store. The exception to
this is with "Wonder" products which incorporate TV Tuners (eg TV Wonders,
All In Wonders and eHome Wonders) because the NTSC Broadcast format products
made for the US and Canadian markets won't tune to the PAL/SECAM Broadcast
format used in most other countries worldwide.
ATI has a facility on their website whereby you can actually compare the
features present on different manufacturers cards going by the "series"
here's a link:
http://apps.ati.com/compare/
Paul