I have a Kona Caldera.
It's a tank (heavy) but has a really nice feel. I'm very happy with it and upgrading it.
BTW I ride onroad/off road, want a road bike but I dont have one yet nad use this with a semi-slick rear all year round (fun fun fun in the mud now!)
The NUNU is a very nice bike.
I tried to get my friend to get one, but he is to cheap and went with a Shwinn instead ;/
Anyway.
I have no experience with Marin but I will stand behind Kona in a heart beat. Very happy customer.
Chad