Shot them both before purchasing... bought a Shield. There isn't much of anything to upgrade on the Shield, it holds more rounds without the cost of aftermarket extensions and has steel sights that are quite usable. The plastic slot fillers Glock issues have to go and that is an additional expense. I bought my Shield ready to go for $360 and the Glock was $440 without decent sights and needing mag extensions. After 600 rounds I'm happy with the Shield, decent trigger and sights, accurate and has been 100% reliable with anything I can cram into a magazine.

Every normal man must be tempted, at times, to spit on his hands, hoist the black flag, and begin slitting throats.