Hi! It really depends on what type of bike and what your intended use is. Bikes of all sizes are incredibly competitive nowadays, unlike 20 or 30 years ago when it was nearly expected that anything for highway use needed to be 750cc or larger.
If you are a newer rider you might avoid full on sport bikes because they are really toned down race machines, and ergonomics suffer. Something like a hyper naked like the Yamaha MT-03. But I'd stay clear of the smaller displacement cruisers, as they have a bit more weight and less HP.
If you are looking at one of the supersport 600s, it's really down to picking your favorite color and features. They really are so closely matched in performance these days it's insane.
