My DD 7.5 has both so here is our assessment.
She is on her second pair of Keens Newport, bought the first pair in June 04 and just replaced them last month, the old one look almost brand new. They are a workhorse of a shoe and super comfy. I like her feet to be cool but protected also. She wears them everywhere, school, canoeing, camping and WDW with no problem. Alot of the summer programs around here won't allow anything but tennies and this style of closed toe sandal. Yes they are expensive ($55ish unless you catch them on sale, I have seen them for $32) but for us they are worth every penny. I have 2 pair myself and wear them from spring well into fall and DH has his also.
The crocs, (I'm still not sold on them, tried them and they made my knees and hips ache after about 4 hours, noone else I know has this problem) but she seems happy with them. She has worn the crocs to WDW but she says school and camping are no good cause she is always having to get the dirt out of them and DH says no to shoes that could float off her feet canoeing.
If I had to pick just 1 for her it would be the Keens, we just seem to get more bang for our buck out of them.
Hope this is more helpful than rambling
Angela