I started on a 2014 Ninja 300. Bought it for $4000 with 1000 miles on it and rode it for a full season. Low sided hard on that 300 and picked myself back up. Sold it for $3600 with 4200 miles on it. I'm glad I didn't go straight to a super sport. I've got about 650 miles on my 2016 636 and the difference is night and day. It's almost like having to learn all over again!
Jmars0990 the difference between the ninja 300/636 is HUGE, in many, many, ways. Like you said night and day. I am breaking in both bikes for my company at the moment on back roads up in WI to prepare for our track riding season as we rent em during our track day and riding clinics at racetracks. Simply awesome machines no doubt. In fact, our 636 will be Jason Pridmore's instructor bike for his JP43 Training school when he rolls with us, pretty much in stock form! It's really FAST.
The increase in torque/hp alone from the 300 to the 636, approx 3x, combined with a more aggressive seating position, clip-ons, means you absolutely will have to continue to learn and start with a new application that is a very potent machine. Respect the bike. The 300 seems like a toy when you spend time on the bigger ninja.
Please be careful; as you already have a low side under your belt, with very limited time in the saddle, the 636 ups the ante big time. Mistakes at this level could be much more damning and painful for you. Go slow to go fast and work on being a smooth rider. Respect the new 636, again as awesome bike. In stock form, without a steering damper, tank slappers can happen, seemingly out of nowhere at speed and you can hit triple digits in nano seconds if you are not careful/ready with a handful of throttle. Even keeping the bike in 8-9k rpm range puts you well over normal speed limits big time and wide open throttle delivers blistering speed at redline. It's really, really fast.
Be cool, keep learning what is goin on underneath you and ride safe. Enjoy the experience of a new motorbike.