Glocks are fine handguns. The first question your should ask yourself though, is "What do I want the pistol for?"

Self defense? Target shooting? Just want one? For example, if you're considering self defense, plan to get a CCW permit, and use inside-the-pocket-carry, then even the smallest Glock will be too big for that. They'd be fine in a belt holster or inside-waistband holster however.

If you're only asking about the functionality and reliability of Glocks, with no specific purpose in mind, then I doubt many would vote against one. Glocks are good guns. If you're "just wanting one" or wanting something for target use, I'd go for the 9mm. Simply because that's the cheapest and most prevalent ammunition. I even works well for self defense, although others may argue for a different caliber. IMHO, differences between things like 9mm, .40s&w, 357sig, .45, etc. are fairly minor in the overall scheme of self defense. They can all get the job done normally. One may be better for this, another better for that, but overall the differences are relatively slight.