Early morning and evening are the best times to see them. I have seen the most grizzlies near Mt. Washbrun and in the Hayden Valley. The Lamar Valley and near Tower are where I've seen the most black bears. I have seen them all over the park though. Mostly it's the right place at the right time. It is especially sweet to be the first ones to spot a bear because you don't have the tourist frenzy going on.