As a disclaimer I'd like to point out that I'm by no means an expert, and that I've been riding for around a year and a half so I'm basing the following blog on my experiences during that time.
In said time I've went from Honda CBR125, Kawasaki Ninja250r to more upright Kawasaki Versys 650. (I'm putting it up in front to let you guys know that I'm not talking out of my arse )

During my forum travels, I often encounter young guys and gals wanting to get into motorcycling world. Which is fine by me, but what bugs me is their choice of a first motorcycle, which is what I want to cover today.

As a general rule of thumb, a 600cc super sport (like an R6 for example) is not the best choice for a beginner due to the aggressive characteristics of the bike. Such bikes require large amounts of throttle control, focus and skill, which a new rider (frankly speaking) just doesn't have.

I believe that starting out on a smaller, lighter 250cc motorcycle (if not 125cc's) or even a 650 twin (and upcoming new 500cc's from Honda),
provides a stable starting ground for a first timer, as they're generally much more forgiving to ride, making the learning curve gentler and easier to follow (let's face it, not everyone's next Valentino Rossi). This will allow said learner to polish up their skills before progressing up.
Arguably making them a better rider in a long term.

Personally I believe that a perfect first motorcycle should be
1. Cheap
2. Preferably naked (no plastic fairing which can prove to be quite expensive
to replace in case you drop it... and that happens to the best of us)
3. No more than 250cc

Starting on 250 is good, but we'll all heard about people who started on 600cc and were fine. That's fantastic, but for a first time rider, putting yourself on the machine that leaves you with smaller margin for error and much steeper learning curve can prove to be pretty bad idea .

I'd like to debunk two counter arguments to riding a 250:

I'll grow out of it quickly - Perhaps, but I've ridden a Ninja for almost a year and I can say that it all depends on your attitude. There's no need for anything more than 250 on the road realistically, and it provides a fantastic learning platform.
Having ridden 125 for few months beforehand I can agree that they could use a little bit more power to get away from dodgy situations (and that's where 250 comes in). And believe me when I'll say that you can have a lot of fun on a 250, and depending on the road, even more so.
Someone once said "It's better to have 250 and ride it to the limit, than a 1000 and ride it like a bitch"

I'm a big guy- Dude. I'm 6'6'' and 275 pounds heavy (I'm on a diet now btw ) and 250r was carrying me happily at 70mph (112kmh) all day long (it topped out at around 100mph btw). Unless you're critically obese, you'll be fine.

The ultimate decision however is up to you: Are you capable of restraint and focus necessary to start with 600's? If the answer is yes, then by all means, go for it.

However if you're not sure, I'd suggest starting on a 250. After all, your first bike,
doesn't have to be your last.

Have a good one, and ride safe everyone.
Knight out.