- Slightly better overall IQ
- Pattern noise in shadow areas visible at low ISO
- Less noise at high ISO
- Much better for long exposures - no ugly, uneven colour cast/glow
- Good live view system
- Half the size, weight and price, but missing certain key features, e.g. good AF
- No pattern noise visible at low ISO
- Slightly noisier at high ISO
- Can produce ugly, uneven glow in long exposures (e.g. star trails, or with strong ND filters, or in natural light just after sunset)
- Live view works, but only just.
- Twice the size and weight of the 5D2
- For the cost of the 1Ds3, you can get a 5D2 and a very nice lens, or two 5D2s...
For landscapes/travel? 5D2 all the way - the long-exposure performance kills the 1Ds3, and the better live view and lower weight of the 5D2 is icing on the cake.
I don't know where you're getting the glow from but, I don't see it.