Odd that they're about the same price... 5D1 is often found used (B&H or Adorama) for $600ish-$700ish, while a 1Ds2 is often $1100-$1400.

Both are only going to be good to ISO 1600 (cleaner than crop), but fall apart at ISO 3200. Both are discontinued, and cannot be repaired by Canon.

If you need the 1D series servo capabilities, pay the premium, but I'm not sure there is any other reason to go 1D over 5D... Perhaps weather sealing, assuming it's still working.

For the 1Ds2 you can't change half the settings without outdated software (supposed last verified to run on XP 32-bit) via firewire. I'm not sure if the 5D has that firewire limitation. You'll need to track down older copies of EOS Utility, as the newer ones don't support these cameras.