They're basically the same. There are a few differences, though.
Sapphire has VIVO support. Asus doesn't.
Sapphire comes with a Crossfire connector. Asus doesn't.
Sapphire is 1 slot. Asus is 2.
Asus has a non-stock cooler that might work better. If you're going to pick up a Zalman anyway, then this doesn't matter.
Asus has some extra driver software, but I don't know if it's useful.
I don't remember the software bundle on the Sapphire.
I think Sapphire only has a 2 year warranty. Asus has 3.
For most users, these differences are negligible. If you want either CF or VIVO or require a 1 slot card to fit in your case, then probably the Sapphire. If you don't, then probably the ASUS for the warranty and possibly the cooler.
Either one will work fine since they're clocked within 1 Mhz of each other and they're the same chip.
One very big issue you missed with the Asus. I've called them about it, but they seriously want to do it this way:
They have 2 x1950 Pro's. The you are seeing now at the 180-190 range, will come with OUT the Xfire connector.
Then, when you want Xfire, you will have to purchase the other, more expensive card, which is packaged with BOTH Xfire connectors. So expect the pricing to end up still at $400 for both.
Personally, I think that is stupid, and i ordered 2 of the Sapph's . Now, if only I could figure out how to get them to work!!
Seriously, 1 has signal during boot up, the other when Windows starts up. And when i go to bios, it acts like it knows both are there, but ONLY the top half of the screen shows the bios, and it has lots of shadow text (the text is displayed normally and shifted to the right in a more ghostly level).
They don't seem to have any heat issues, so at this point, I'm very happy except for trying to figure out why i can't see bios and windows from both cards at the same time, or one all the time.