^+1, I'd pick the Corsair.
I prefer the Corsair, but would take the Antec in this situation.
It's going into a Dell, the cable sleeving and longer wire lengths on the Corsair make it more difficult to route and hide the wires.
The warranty wouldn't be voided, it just won't cover the psu.
If you needed to call Dell support for a hardware issue they would request that you put the original psu back in so that the upgraded unit could be ruled out as being part of the problem.