I love my Glocks and as much as I love Ruger products (I own a GP100 and Ruger 10/22), when its handguns that are semiautomatic in 9mm and .45ACP department its the Glock 17 and 21s for me.
Glocks are great BUT there are 3 things I wanted to fix ergonomically:
1) The trigger pull was a bit much so I replaced with a 3.5 pound trigger connector.
2) The slide release latch is a bit small, aftermarket one with a little 'bump' fixed it (you can see on both Glock 17s).
3) The mag release is a bit small so I replaced with extended one, rounded off the slightly sharp bits with a 400 grit sandpaper.
All of the above can be done in about 15 minutes but I took my time and took an entire evening to get it all just right.