Do some research on the Horizons Unlimited Forum. Everyone there are long distance overlanders, many have crossed continents and some circumnavigated the globe. The bikes used range from Vespas to sport bikes. When asked why, the standard answer is either that's what I could afford or that's the bike I owned when I started.
https://www.horizonsunlimited.com/hubb/which-bike/A couple of extreme examples of people who rode whatever they owned:
1.
https://teapotone.com/ Bruce aka TeapotOne rode a Superbike 74,000 miles solo around the world, through 54 countries in 442 days. Over a beer Bruce explained that he owned the GSX-R 1000 at the time his journey started and couldn't afford to buy another. He traveled the world on this bike wearing leathers.
2.
https://www.worldvespa.net/ Alexandra, Stergios and “Kitsos” their Vespa scooter, two up from Greece through Africa and across to South America and still going. It is incredible what they load on that Vespa! If you ask Stergios why the Vespa he explains that he sold everything he owned when the Greek economy tanked and kept the Vespa he used to ride to work and simply started the journey.
3.
https://www.2ridetheworld.com/ Simon & Lisa Thomas who initially planned a 16 month trip have been overlanding since 2002. They started with a BMW 1150Gs and an 650GS and in 2016 traded for two new 1200GSA’s after 14 years on the road. Apparently BMW’s are not a good choice for this kind of trip! These two have traveled through 80 countries on 6 continents.
There are pro's and cons regardless of the choice you make. Smaller is not always better, especially when riding solo and carrying everything you need. New is not always bad. Many examples of modern bikes filled with electronics crossing continents. It will come down to what you are comfortable with given what you can afford considering where you want to go.
Here's a most interesting article on lessons learnt:
https://www.madornomad.com/sam-manicom-8-lessons-from-8-years-on-the-road/Lesson one: Pick a bike you love and go!