Is it a cop out of an answer if I say all of them?
Why limit yourself to a subset of the globe when you can see it all? This is all hypothetical, isn’t it? Spin a globe, stop it with your finger at some random spot, go to that place. That’s how it’s done, folks.
If we are going to limit ourselves to some hypothetical subset…
I’ve only been to one country outside of the United States and that was Canada. As I am a little on the lazy side when it comes to traveling, all of my top choices of countries to visit would likely be places where most folks speak English, and most road signs are also in English. The UK and Ireland would all more or less tie for first place on the big destinations list. Australia and New Zealand would be on the short list too, but only after the British isles. After that, how about literally everywhere in Europe. Start in the West and work my way East. Simple.
After that? I really don’t know. Brazil, Morocco, India, Japan. Maybe a road trip from the Southern tip of South America all the way home. That would be pretty fantastic. Then we could rerun the plan starting at the Southern tip of Africa and ending in France or Spain, and then fly home from there. Just imagine how much the rental car would cost for a trip like that. Yikes, but totally worth it. It would make our epic drives to and from Disney look like a walk around the block.
I’ve kinda gotten off subject though, I think. The short answer to the which countries would I like to visit question is every country in the British Islands and more of Canada. I want to go to Newfoundland, where my maternal grandparents came from, and Ireland, where my paternal grandmother came from, and Scotland, where Jen’s family came from. I want to trace our roots, as it were. That would be fun.
We have to go back to Disney World twice before we leave the country though, and after that we need to go back to Southern California which will likely include a day trip into Mexico… which just implies that any plans I have for international travel are likely to never get too far beyond hypothetical. It’s like John Lennon said, life is what happens when you’re busy making other plans.
Inside the Red Head's Head 
I’m very much the same in this regard. the only countries I’ve been to are Canada and France.
France was school trip. Windsor, Ontario is just in the other side of the Detroit River, so crossing was very easy pre 9/11. We would go there because Canada’s legal drinking age is 19.
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