Yellowstone - Spring or Fall?

We were there about 2 months ago - we stayed at Yellowstone RV Park at Mack's Inn; about 25 miles south of West Yellowstone. We decided rather than dealing with figuring out what to see, when to see it, and where to park we went with a bus tour through Yellowstone Vacation Tours in West Yellowstone. The bus is a 24 passenger van, and our guide, Matt, was outstanding! We boarded the bus at 8:00 am and were back to their office about 4:00 pm. The tour we selected was the Lower Loop Tour, which includes 4 different hot springs areas, Old Faithful, the Grand Canyon of the Yellowstone, and lots of wildlife. We even got a special treat: we arrived at Old Faithful about 10 minutes before it's scheduled eruption, and got to witness the Beehive Guyser erupting - it on it's own schedule: about every 23 hours, give or take 10 hours!