S.,
Yellowstone National Park is a great vacation spot. My husband and I love to go there on vacations. We have stayed in Jackson Hole and driven up from the Grand Tetons. We have also stayed in the little town of West Yellowstone on the North side of the park. There are lots of great hotel options for every imaginable price range. The real issue is when you want to go to the park. There are more hotels inside the park that are open during the high tourist season. There is a spectacular twig style Victorian hotel built about 1899 right next to Old Failthful that is only open in the summer.
The closer you get to the summer tourist season the more people crowd into the park. Summer can be a zoo, the roads are mostly two lane and just driving through the park will take you all day. Finding a parking spot to walk out to the look out points can also be a chalenge. The park in winter is completely different. We used to go snowmobiling in and around West Yellowstone in mid-February as well as through Yellowstone. The park is almost empty and while you can't hike into the back counrty easily you can get to all the same spots most of the summer crowd gets to see.
Having seen the park in the summer and winter I can honestly say no matter when you go it is worth the trip. However, I have to admit my favorite season is winter. All the boiling mud and water creates massive collumns of seam. The animals move onto the roads to move around so you can come around a corner and suddenly be surrounded by a herd of buffalo. The elk come down from the mountains, there are geese, and swans on the Fire River. The entire park feels like you just stepped into a crystaline fairy tale.
My best piece of advice is to buy a National Parks Pass if you do not already have one. They are $50 for the year and you get access to All the National parks. Addmition runs about $25 dollars per car so all it takes is a visit to three parks and the pass has paid for itself. If you have any other questions you can email me at ____@____.com
Have fun!