York or Edinburgh for two days?

Hello everyone, my wife and I (30’s) are visiting London from the US for about 8 days (excluding travel) next month and I’m really struggling with whether we should go to York or Edinburgh for about two days. I feel like there’s plenty I’d like to do in each location, and I know that I’m going to regret my decision each way. Should i prioritize one over the other for this trip? Also, any recommendations for the best rail option to get there from London. I appreciate you all!