Both are just as interesting, Vietnam is more bustling especially Ho Chi Minh, Hanoi was more laid back. The arts scene is very interesting, somehow everything just feels more refined and gentle. Cambodia has plenty of lots of historical sights... be prepared to climb some very steep steps... bring some Bengay with you if you are as unfit as me. Vietnam will be a better bet with kids as I feel that they are more amenities there and there are better chances of getting reliable baby products there. The last time I was in Cambodia approximately 2 summers ago I remember seeing swamps of mosquitoes in a 5 star hotel (Hopefully they got that under control now)but I remember that Raffles did not have such a problem as they scented the entire hotel with citronella.