It just depends on how long you can spend, when you want to go, what else you want to do in the state, & what your physical level is. For me my favorite time is early September after Labor Day. I recommend 3 days in the valley & at least a day in Toulumene Meadows. If you're going to camp, reservations open up 6 months in advance. The Toulumene Meadows campground will be closed till 2024 I think. If you are thinking about hotels, consider Curry village in the park.