To be honest, I think I'd rather them open with TKH rather than UAGM. It's a good song, but it's not really that good as an opener. Or maybe switch UAGM for OTBOA.
Would be kind of weird to start the show with the one track from their new album, though, don't you think? I think they've placed it in a great part of the set--they play it right in the middle, after the crowd's been energized, but before they get to the ending songs. Some of the fans may still have not heard it yet, too--would be weird to open with a song that not everybody knows. Given the way the band sort of slowly comes in, it IS a good opener, but it'll fit better in that slot once the new disc is out.
TKH--meh. The LATM version of that song is possibly my favorite DT song ever, but I highly doubt James really could pull off that sort of performance, especially every night. And without that, it really isn't worth playing--again, many fans (even on this forum) haven't even heard it before.
All things considered, I think UaGM is a good choice. Let James get some of his more demanding vocals out of the way early, play a song everyone knows, etc. It doesn't drag, its intro develops well, and just about everybody likes it. The only other serious options would be something overly long like ES, TMOLS, or TCOT, something shorter like Forsaken (which wouldn't start the show off well to the "Ugh, SC" crowd) or one of the overly-MP-influenced songs like NE or TGP. PMU and LtL would work too, but I'm sure they're sick of PMU, and LtL is closing.