Boy, you are really going to start a war here!
In my opinion (it is very biased toward the H&K I'll warn you in advance), its a toss-up.
The GLOCK tenifer finish would probably win out for effectiveness in harsh environments, but H&K will hold its own assuming the guns are cared for. H&K's are available in stainless which would make it easier for it to compete in the harsh environment arena.
For reliability, GLOCKS have a great track record, but though they are not as popular, the H&Ks are superbly reliable as well. I'd say it would be a toss up here. I seen one (of many) H&Ks fail to feed. The round that wouldn't feed was a PMC fmj that was subsequently tried in several GLOCKs and a couple of Hi Powers and failed to feed in all.
Ease of maintenance would be a toss up for field stripping, but for full disassembley of the frame, the edge would probably got to the GLOCK (H&K has more parts).
Service life would be equal in my opinion.
That being said, I would pick the H&K because I shoot them much better than the GLOCK. As close as they are, I would shoot them both, pick the one I liked best, and not look back. Or, buy both!
Shake