Portugal and Spain advice

Looking to plan a trip with the family in June where we either start in Portugal and sightsee our way to Barcelona or vise versa. Any advice on which way is better? Is that too far to travel only by train? What are the best stops in between? Any suggestions on great places to stay? Any help is appreciated, I feel a bit overwhelmed trying to plan this but I have promised the wife This trip for years and I need to make it happen.