Get the 5D. The original 1DS might be around the same price, but it was the first FF digital camera that Canon developed and marketed, so it comes with all the pitfalls of being...first.
While its body is more rugged and sturdy than the 5D, it has worse low light performance, less resolution, smaller, lower quality LCD, and its batteries aren't great, especially given how old many of them are.
You see, the 1D series until I think the Mark III used nickel-metal hydride batteries. As these types of batteries age, their ability to hold a charge dwindles until they become expensive paperweights.
Besides that, the button layout on the 1D series is MUCH more cumbersome than on Canon bodies that have a more conventional DSLR form factor. To change ISO, for example, it requires you to hold down two specific buttons on top of the camera, and then use the wheel on the back or top to change it. It's a very unintuitive layout when compared to the 5D series.
They didn't simplify it until the 1D/S Mark III.
As someone who has used the 1DS, 1D Mark II, and 5D Classic, if you don't need speedy autofocus and a DSLR chassis that can survive a bomb blast, you'll probably be happier with the 5D.