I’m a big fan of Yamahas. Except for The Honda that Wouldn’t Die (a 1979 CX500), all of my bikes have been Yamahas; starting with Enduros (street-legal dirt bikes) and currently a 600cc Seca II.
I’d suggest getting a 600cc street bike. While a “sportbike” would be nice, my “standard” Seca II has been the perfect bike for getting around the L.A. area. I’ve ridden it from Los Hideous to Novato (north of San Francisco), Las Vegas, San Diego and Lake Havasu too. A 600cc “standard” bike has all the power you’ll need, is economical, relatively inexpensive to buy, and won’t rip your arms out of your sockets while you’re learning to ride.
As I said, I love Yamahas. But Honda has a reputation for superior reliability. They have a 750cc Nighthawk that is a “standard”. Once upon a time its style was called the UJM: “Universal Japanese Motorcycle”, as all of the HYKS (Honda, Yamaha, Kawasaki, Suziki) bikes looked pretty much the same. The Nighthawk retains this classic look. Yamaha’s standard-class bike is the Seca II. A couple of years after Yamaha came out with the Seca II, Suzuki built a clone called the “Bandit”. I’ve heard it improved on the design. I’m not familiar with the Kawasaki standard.
There are a lot of cruiser-class bikes out there. IMO, they are not as stable as standard-class, but they’re more comfortable for extended riding. They’re also very trendy now and a lot cheaper and more reliable than a Harley Davidson.
Expect to be “behind the bike” at first. I was surprised when I switched from the CX500 (a mini touring-class bike that looked like Honda’s version of a Moto Guzzi) to the Seca II. The lighter, more powerful Yamaha did jerk my arms a bit the first couple of times I took off.
You’ll have to develop a new set of instincts when you ride. Things can happen quickly on a bike. I see a lot of “left-seat zombies” in the 90-100 miles I drive every day. They’re just not paying attention. When you ride, you’ll need to look out for them. You’ll also need to get rid of any zombie habits you may have. Thinking ahead can keep you alive. Things that wouldn’t concern you in a car are very important on a bike. If you “panic brake” a car you don’t have to worry about the car slipping out from under you. A bike can go on its side. You probably aren’t concerned too much about dirt or gravel on the road. If you’re on a bike, you need to be aware of it, as the bike can slide out from under you in a turn. I started riding when I was six. I developed my “riding instincts” on slippery, rock-strewn dirt roads. But I’ve gone down on the Seca II. I hit a flattened aluminum can that I didn’t see in a left turn and the rear wheel slid out from under me.
I’ve never ridden a scooter, but they seem to have a high centre of gravity. They might be more efficient around town, but I prefer a “real” bike. And don’t ignore the freeway. I think it’s safer than being on the street since everyone is going in the same direction and there is no cross traffic.
Most important thing to remember on a bike: It’s supposed to be fun! Have fun.