A lot depends on how you plan to use the bike. Just on the road, just off road, or a combination? Low speed around town or will you be doing some highway miles? Also how tall you are has a lot to do with it.
Generally speaking, you should start on a used motorcycle, because you're likely to be very hard on your first bike and it would be a shame to screw up a brand new one. Get something 5-10 years old (old enough to be depreciated, new enough that you can still get parts). After a year or so you can sell this bike for about what you paid for it, and by then you'll know better what you really want.
All the Japanese makers are very good. Harley and BMW are also very nice, but EXPENSIVE. Japanese bikes are a much better deal for the money. I think Honda is best, but I'm prejudiced 'cos I own one and it's been just extremely reliable.
A lot of people here will say you should start on a 250. A small bike is better because it's lighter and easier to manage, but a 250 is not big enough to cruise at highway speeds. If you plan to do 20 or 30 miles at a time (or more) at 60-70 mph, a 250 is too small. A 500 or 650 would be better, and it's not that much bigger or heavier. Good models are the Honda 599, Suzuki GS500 or SV650, Kawasaki Ninja 500 or 650r. There are a lot more in this category.
You want to be able to sit on a bike with both feet flat on the ground. For 'inseam challenged' people, this narrows the field somewhat. Cruisers have the advantage here, because they have a lower seat. All motorcycles publish the seat height in their specs, but the seats are all shaped differently so you really can't tell unless you actually sit on the bike. Cruisers have other advantages--lower center of gravity, more relaxed steering geometry, etc.--so you could go even bigger, a 750 wouldn't be too big to start with. Honda Shadow, Kawasaki Vulcan, Suzuki Boulevard, Yamaha 'Star' all make a moderately-sized bike, 650 or 750 or 800cc.
If so, I'd suggest you get an older japanese bike. Something 500 cc or smaller. They are generally fairly cheap, and if you happen to drop it, you won't ruin new paint. Then once you're comfortable with that you can sell it for about what you paid and upgrade if you want. But no sport bikes. They are far too much for a beginner. That would be like learning to drive car in a Ferrari.