As the ATI brand has been phased out long ago by AMD, using the amd-graphics tag would be recommended.
Ubuntu provides open source (default) as well as proprietary AMD graphics driver packages for installation. You can also manually install the latest beta drivers from the AMD website. Take a look at the Binary Driver How to AMD article from the Community Help Wiki for instructions.
Note: That there is sometimes a delay between newer graphics cards beeing released to market and compatible graphics drivers for Linux becoming available. This is also true for newer Ubuntu releases which feature a new graphics stack that may be incompatible to older drivers and leave you without a working GUI.
ATI Technologies Inc. was a semiconductor technology corporation based in Markham, Ontario, Canada, that specialized in the development of graphics processing units and chipsets. Founded in 1985 as Array Technologies Inc., the company became publicly traded in 1993 and was acquired by Advanced Micro Devices (AMD) in 2006.