I'm a pretty poor judge to be honest as the number of countries I've visited can be counted on one hand.
That said there are a few places I would love to see, I'd like to go and see my friend in Brisbane some time. As I work in physics it'd be good to go to Switzerland to see CERN and what goes on there, at the same time Florida has the Space Center. Not only that, before he retired my grandad loved living in Florida, my mum lived there for a year too and now my grandad has passed away it would be good to see where he spent his best years.
So they're my top 3 places I'd like to visit, in order I'd say:
1) Florida, USA
2) Geneva, Switzerland
3) Brisbane, Australia