we all know the ironhorse is world cup tested, it kicked ass year after year. the demo on the other had hasnt raced the world cup til this year when it was redone for sam hill and the monster energy team. so i have to say sunday for the win on this one.
All comments this far have been on personal preference, so i'll give it a shot.
The Sunday is a racing bike. The DW-link works great at high speeds, it has little pedal bob and is fairly light.
The Demo is a more freeride oriented bike. it is a do anything bike, I'm not saying the Sunday isn't, but I would pick Sunday if I were a racer and Demo if I was a "do anything" guy.
No matter which one you choose, to be honest, the biggest difference is their looks, it isn't so much difference in suspension and geometry. They are both great bikes that you will be very pleased with.