I am using the Ti 4400 128MB. It's the slower memory on the Geforce cards but that was easily solved with an overclock. I had too much trouble with compatibility in the past with ATI cards so I am partial to Nvidia cards. I would say go with the Geforce FX cards. They are beaten by the radeons sure, but not much. And will you really notice the difference?

PS when I get around to finishing my daughters computer, she is getting my ti4400 and i am getting the FX5600