What is best way to Juizhaigou traveling from Xian? Happy to stay 1-2 nights somewhere along the way

I think the best way is to fly from Xian to reach there.
If you want to try other ways, you can take trains to reach Chengdu and then go to Xinnanmen Bus Station to take buses to reach JJG. If you choose the second way, you may have a chance to visit Chengdu and stay there for a night.

Thank you for your reply. I am not really interested in staying in Chengdu. Is there anywhere on the way to Chengdu that is recommend to visit for a night?

If so, I think Mianyang is nice for stay a night. The environment is very nice and the local parks are worth seeing.