I would base your decision on mobile coverage and the monthly plan. The Atrix, from what I've read, is a superior phone to the EVO. I have the Atrix and love it, but have never owned an EVO. To me, the EVO is just too big a phone. Now, you might be able to work with AT&T to give you an unlimited plan that matches up with your current Sprint plan if the company you work for has a premier relationship with AT&T, in which case, I'd say Atrix all the way!! I've been with AT&T for 16 or more years as a premier business customer, so I've been able to maintain my unlimited data from device to device without any problems. I just moved from a 3GS to the Atrix....the experience is a lot different....some things great, some things not so great.
HTC TILT 2
ROM: AT&T Stock ROM (not bad....a little bloated)
ROM: Personal Cooked ROM (WM6.5 21857 Edition)
MANILA: Gen.Y Manila "Revolution" R1.5 VGA Port CFC