I have a G19 2nd Gen and find it to be a great reliable gun. The grip length is a bit short for my hands but that can be fixed with a pierce mag extension. As for .40 vs. 9mm, the 9mm is way cheaper to shoot than .40 I you can rent and shoot both then decide. Check this out if you have doubts about 9mm abilities.
http://www.brassfetcher.com/index.html