what's the difference-Riva tnt, tnt, tnt2

I am not a video card expert and i am now paying the price as i learn. Can anyone explain the difference, and give a general performance recommendation between them?

all TNT chips have integrated RAMDAC, Pixel unit, and dual TMU, as well as 128-bit memory pipeline.

Riva 128 -> ~55MHz clock, single TMU, competitive with Rendition chips and Voodoo Graphics. 64-bit memory pipeline and PCI busmastering.

Riva TNT -> ~90MHz clock, originally was supposed to be 100MHz clock but dropped at last second
250MHz RAMDAC. Comparable in performance to an overclocked Voodoo2 but with better image quality.

TNT2 -> 125-150MHz clock depending on board vendor (set in BIOS).

TNT2 Ultra -> 150-175MHz clock depending on vendor.
300MHz RAMDAC on all TNT2 chips.