As far as reliability goes, Glocks are second to none. A G21 (.45 ACP) is also nearly half the price of a good 1911. The double-stack magazines carry nearly twice as many rounds to boot.
I carried a 1911 for two years in the military and loved it. However, most of the commercially sold models are not nearly as reliable, especially out of the box. They often require a lot of tinkering (springs, feed ramps, after-market mags etc.) and many manufacturers will recommend a 500 round "break in" period with FMJ ammo before you can expect performance. That recommendation was actually in the owners manual of a Kimber 1911 I had.
Being intimate with both weapons, for serious defense the Glock would be my choice hands down.
When were you in the military?