Ahh you beat me to it. I was going to start a similar thread. I would categorize into 125-250cc and 400-500cc and have the bikes listed with pros and cons. Feel free to add this to your post if you feel its helpful.
Anyways, I believe the 250s and 500s are good starting bike. I dunno about the 650s....they could be a good bike to upgrade to after some experience on the 250s but thats upto the rider. I've broken down
the battle of the 250's:
Ninja 250r: Most popular bike out there and easy to re-sell with minimum loss. Its a two cylinder, 4 stroke, liquid cooled engine. Its has the most power of the three but for some weird reason is not fuel injected. The europeans get F.I. bikes, why don't we? So that means you've to play with the choke to get it started and its a hassle especially during cold days where you've to warm up the engine for a good 5 minutes or more. This bike is slightly wider and heavier than the honda by 20lbs. This is good for taller ppl like myself (6 feet, 185lbs).
Honda CBR250r: The new competition for the ninja and it a strong competitor. Though its slightly slower than the ninja with single cylinder, 4 stroke, liquid cooled engine; its got an edge by being fuel injected. What that means is no worry's for cold starts or warming up the bike for a while before heading out. This right here would one big reason many people opt for the Honda over the Ninja. Also this come equipped with optional ABS which the ninja doesn't offer. Being single cylinder, its narrower and lower to the ground ideal for medium to short height people. Also this has the most torque of the three but also the least power of the three.
Hyosung GT250: Its a two cylinder, 4 stroke, air cooled bike. I've heard lot of problems with air cooled bikes and I usual tend to stay away from them especially if you have a lot of stop and go traffic. I've also heard the ride and fit/finish is a little below par. Hard to recommend this bike, plus the resale is hard. Power and torque puts this in the middle of the other two bikes.
Here is quick link for video shootout and article ->
link