Here are the facts, straight-shot and completely unbiased:
1) A Ti4400 is clocked at 275/550. A Ti500 is clocked at 240/500.
2) At the same clock speeds, a Ti44/4600 is 20% faster in benchmarks and game demo-benchmarks than a Ti500.
3) A Radeon 8500 is roughly as fast as a Ti500.
4) A Radeon 8500 is not designed to take advantage of 128mb of RAM. It benefits little from it according to benchmarks and reviews that I have seen (2-4% maximum).
5) A Ti4400 runs at 275/550, and is 20% faster even at the same clocks as a Ti500. The Ti4400 is about 35-45% faster than a Ti500 according to benchmarks.
6) The GeForce 4 core is very efficient at antialiasing and true anisotropy, unlike the Radeon's rip-mapping which doesn't apply anisotropy to anything at a 90 degree angle to the floor or a 90 degree angle from your viewpoint.
7) A GF4 Ti4400 is about 70-80% faster than a Ti500 in AA/anisotropy. A comparison to an 8500 is an apples-oranges comparison as the ATI card doesn't apply true anisotropy to a scene. In addition, the 8500 offers odd AA modes, one being a "performance" mode that does almost nothing at each setting, and one being a "quality" mode which is very slow at each setting of AA compared to a Ti500 and is slightly (negligibly) worse than a Ti500's antialiasing quality under magnification in screenshots from identical positions (such as a level startpoint, etc.)
8) Seeing as how the Ti4400 isn't much more expensive than a Radeon, judging by these facts, it is a better value and will last you longer. The extra horsepower, as well as AA and anisotropic performance, will provide a longer-lasting value and be able to cope with games such as Unreal Tournament 2 coming out in June and other games of demanding levels such as that coming out in 2-6 months from now. Benchmarks of the cards on the Unreal Performance Test, utilizing the Unreal 2 game engine, show that the Radeon isn't capable of providing an acceptable (by even the lowest definition, 30fps or higher) frame rate in the games coming this and next quarter utilizing DX8/8.1.