'Grüß Gott' is often used as greeting on Bavarian trails. From my limited experience, it's most often used by older people, younger use 'Hallo' more often.
I don't feel 'Hallo' is very adequate to greet older people, so I'd find 'Grüß Gott' better, but I have a doubt - is it considered religious-neutral nowadays? Or by using such formula, you express some kind of commitment to the faith?
I'm very little committed to faith, so I just don't want to make false impression. For example, I wouldn't like to express my wish to speak about God just because I've used that greeting for absolutely secular reason ;)