I wouldn't say those two cards aren't really budget, i'd say they are "bang of your buck" cards.
I'd probably go with the x1900xt only because ATI gives you the added bonus of running HDR & AA at the same time. You will have a slight drop in frame rates with both enabled, but if you look at screen shots you can notice a difference. It's small but adds to the value of the 1800 & 1900 cards.
Unfortunately, NVIDIA 7800 & 7900 cards don't offer HDR & AA at the same time.