I would go to SEA because it's winter. Go to europe in the summer. To be honest the magic amount of time for me is 1 month in 1 place. You can usually rent a place for cheap if you stay 1 month. You can get to know the area and culture, and it's not too long that you will psychologically slack off, because you will know in the back of your head that you will be leaving in a few weeks. Then move to another place for a few days if you like it stay for a month if not check out another spot.
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