Of all the bikes I've owned over the years - around 15 or so - the largest displacement was 850cc - a Norton Commando Interstate - and it was more than enough, and would be even now if I hadn't sold it. A mistake but oh well.
I have difficulty justifying the need for a large engine, a gazillion horsepower and low fuel mileage when a 650-750cc engine will do all I want, or wish to live with at age 67. In fact, of all the bikes I've had, the two that were the most fun were a Suzuki T500 two stroke twin and a Suzuki GS450 four stroke twin. Granted I didn't ride them around the world but they were immense fun for everyday use. Oh, I did ride the T500 from San Antonio, TX to Grand Forks, ND one year and it and I did just fine. No cruise control, no fairing, no GPS, no ABS, not much luggage carrying capacity, but it was a blast and I could end the day and still climb off and be ready for the next day. Sinplicity has its place.
My most recent short list, before buying a Versys, was the Versys and the 650 V-Strom. The Versys won the battle because it fit me, and was, I thought, easier to handle. The 1000cc V-Strom fell off the list quickly because it was just too heavy and cumbersome for me - and it drank fuel faster than I thought it should.
It strikes me as humorous that most motorcycle magazines consider mid-displacement bikes (like the Versys) as entry level machines. I'd prefer to think of them as sensible machines. They're better than the old liter bikes - they handle better, get better fuel mileage, are easier to maneuver, stop better and are easier to live with day to day (for the most part anyway).
After all this, my point is that a modern 650cc machine is really all that the average rider really needs - unless you rack up 20,000 miles of long distance touring each year or need to cruise at very high speed, or simply want to impress people. My two cents worth concerning what is probably an unanswerable question. Hope you enjoy whatever you decide on.