I've previously used a motorcycle for basic transportation; also, I've done several cross country (coast to coast) trips, some with a passenger. I've ridden through deserts and mountains, sand and snow, and have sewn a few curves together. My minimum threshold for long distance riding, especially with a passenger, is 750cc with 4 cylinders. Safety is the primary concern. Regardless of how defensively you drive and who has the right of way, you need enough
responsive power to get out of the way of heavier enclosed vehicles. Additionally, there is a marked difference in comfort between a 4 cylinder engine and a 2 cylinder thumper as you rack up the hours on a long trip.
If you're primarily riding alone on short commutes and/or joyriding with a passenger on short trips during light traffic times; then, a 550cc - 650cc will suffice and the number of cylinders becomes less important.
Just be sure to buy enough bike for its intended use or you'll later be disappointed regardless of its initial appeal.
