If your work takes you outside of the country the Photon with its global GSM sim capabilities is the way to go. Other than that I'd say both are excellent devices, don't think you can go wrong either way. I currently own a Photon but I'm switching to the Galaxy SII Epic Touch 4g for the Amoled Plus Screen. My friends tell me I'm insane but as a graphic designer and a photographer I notice the pentile matrix on the Photon's screen and it drives me batty. They don't notice it, but I do. As mentioned before call quality on my Photon has been outstanding, fantastic battery life, really the entire experience has been great. The only reason I'm switching is just the screen which may or may not be an issue for you.
As always best advice would be to go check the two out in the sprint store and see which one you think will work best for you.