My favorite is an easy choice. . . as I only have one international trip in my past.
It was a good one though as I spent close to six months making a ring around Central and Eastern Australia. Not all of it was spent backpacking -- parts of the trip involved long drives on a motor coach while sleeping in tents along the way.
This was back in the late 90s so I'm not sure what has changed (virus or otherwise) since then, but Australia had a lot to offer in terms of scenery and variety. National Parks covered rain forest, mountains (Australia's version anyway!), desert, ocean, natural/cultural sites, plus much more than I can ever remember. I'd gladly go back. . . but the plane ride is something I'd dread.
Positives I remember were a favorable exchange rate, no need to learn a new language, the smell of eucalyptus, wildlife (exotics to me) was everywhere, and the people I met were always warm and welcoming. Negatives included the aforementioned plane ride, at times sweltering heat, flies, and snakes. A lot of snakes. In the central outback I'd often wear a head net to keep the flies away, but after awhile I remember being getting used to them.
A pic (of a pic) I from my photo album. There should be an eleven in front of the 70 on the St. Mary Peak sign -- couldn't see that unfortunate knee placement in the days before digital!

(Mullets are still cool, right?)
Flinders Ranges NP was just one of many I was able to visit. I actually bushwacked part of the way down on this trail and crossed paths with a rather large King Snake -- something I still shudder to think about today.
A picture of my tent at one of the caravan parks during one of the coach drive portions of the trip.
Because Hawaii was in the way of getting home I also decided to stop and spend a week there. . . not international and more car camp than backpacky. . . but a bit of a bonus if you are returning to the states via the West Coast. The Big Island was definitely less touristy and you could camp near the beach in many of the state parks.
