I carried the Glock 21 when I served on a SWAT Team. Never had any problems with it and I saw a guy drop one off of the third floor of a training tower onto conrete. The concrete showed more damage than the gun. (That is no exageration!)

I've never handled the Walther but I can't say that I've heard anything bad about those.

There are a lot of guns out there that are more refined than the Glock but, as a range instructor one of the advantages of the Glock is that they are simple and almost anyone can pick one up and shoot it.