This is kind of lame, but probably the US. 3 weeks would be enough time to take road trips around the country, maybe fly hear and there, and you'd see loads (beaches, mountains) and visit everyone you know. Also, I have discovered that I tend to get weary early when I'm travelling somewhere that I don't know the language. I don't know if I could do 3 weeks in a non-English speaking country.
Do you go to family reunions?