What is best time of year to visit the National Parks (Yellowstone, ect. ) and best tour packages by bus
The best times to visit national parks, like Yellowstone is the beginning of June or in mid September. The reason is because the weather is great, the scenery is beautiful and the animals can easily be seen out in the park. You can choose the best tour packages by visiting a site like http://www.tours4fun.com/yellowstone-tours/?gclid=COD_xty_pbgCFdQgtAodSBsA6Q#cp-35/s-7d/.
I wouldn't take a tour bus ... unless you want to be totally dependent on THEIR schedule.