The Para probably wouldn't be as reliable as the rest, with the comparatively delicate LDA and somewhat wobbly 1911 operating system, so it would get knocked out.
The Glock would probably be marginally the most reliable, but it also has the least comfortable grip to shooters lacking big hands.
The XD and M&P would be strong contenders, but I suspect the XD would win out just based on the XD .45's short but excellent history of reliability and trouble-free service.
The FN would have the backing of the Army, just because FN has been in bed with the military for so long, with the M249, M240, FN303, and M16A2 contracts.
If I personally had to pick one of these for general issue - not that I think a .45 is a great idea for that - I'd pick the XD.
Somewhere, I can hear Jeff Ward cackling.