Adventure or dual sport motorcycles can be great bikes for beginner riders. They can allow a new rider to experience riding in an open field, or trail, as well a get a feel for the bike on asphalt too. If a new rider falls over during the learning phase this is not such a big deal on a dual sport bike. Many of these bikes have protection on them and can withstand a drop which can be common when someone is riding for the first time. I recommend getting a reliable quality used bike, many people buy a new motorcycle to learn to ride and then want to move up to a bigger faster bike, or they realize that motorcycle riding is not their cup of tea and end up selling the bike in great shape with very low milage. So quality adventure or dual sport bikes can usually be found pretty easily on craigslist, cycletrader, etc.
The smaller cc bikes, like the 200, 20 or 300’s are great bikes for learning as they are light and nimble. The big Japanese motorcycle manufacturers all have these entry level bikes.
Honda has the CRF250 i standard version and Rally Version. Standard is top pic and the cool rally version is to the right.
Kawasaki has the Versys 300 now, which is more of adventure bike than a dual -sport, but they had the KLX 250 for a while, which was a great light dual sport bike, but they discontinued that bike. they can still be found around and are good bang for the buck.
Suzuki’s 200 is the DR200, a great reliable starter bike at a price point that is affordable.
Yamaha has the WR250 which is pretty much a dirt bike, and probably the most advanced one, which may make not as much of a learner bike as the others.
Now two of my favorite beginner bikes are the fat tired Yamaha TW200 and the Suzuki VanVan200, these are great for the sugar sand here in New Jersey, but they are fun and easy to ride anywhere and on many types of surfaces. They also have a low seat height and the power is not abrupt and easy to learn how to release the clutch in smooth manner, which can sometimes be a challenge for people who never used a clutch before. These two 200 cc fat tired bikes are a blast to ride and have ton of character too.
So, in short, look for a bike that has low seat height, can be dropped, can ride on mixed surfaces, and doesn’t hurt your wallet to bad if you do break a part on it or scratch it up.
It is always good to take a class, the state motor vehicle center usually run motorcycle classes here is the US, as well there are a number of business that train riders of all different skill levels.