Everybody's different. Our position is, if it has two wheels (sometimes three!) it can't be bad. There are many different styles of bikes (ranging from scooters to trail bikes to sport bikes to cruisers to touring bikes and hybrid combinations like "sport-touring" or "dual sport" and specialty bikes like racing bikes, choppers, mini-bikes), lots of different brands, they're made on all the different continents (except maybe Antarctica!). Part of the fun of motorcycling is deciding what bike you want by going to shows and shops, reading magazines, doing demo rides at dealers and chatting with other riders.
We can't tell you to buy a new bike or an old bike, to spend $30,000 or $300, to get a 50cc motor or a 2300cc monster (you can get a V8 in some custom bikes!). The type of bike you buy depends entirely on what style of riding you want to do. It's our experience that people's riding evolves, so many riders change bikes from time to time.
Our instructors are all motorcyclists. And they're all different. Ask them.
Tell you what: here's Humber College's official position on this question:
"Buy a bike that matches your eyes".