That's an excellent discount! Wish my employer helped me buy my bike :-D

For road commuting you don't need a suspension fork... for offroad you'd like one that has some damping. The Redlines that you link have oil damping forks with lockouts for smooth roads, while the others just have springs in them and no lockout. The first Redline is 9-speed and the second is 8-speed which explains the price difference. 9-speed stuff is generally a little higher quality just because that's what the manufacturers do to us, the jerks. But it's not a super important difference. I can't really see why the D'back costs more than the Redlines, it's a lower spec bike. The only advantage it has for commuting is the smoother tires, which a dealer might swap out for you at a discount.

Be sure to budget for lights, a way to carry your stuff, and tools or a backup plan in case of weather or breakdowns.