This really depends on your experience. If you have been riding a long time, you probably wouldn't be asking this question; so I'll assume that you are getting started and have ridden some. Also, you'll want to consider what kind of riding you'll be doing. If you are trail riding, I recommend looking at the Honda CRF line. I have a Yamaha TTR125 that is a play bike, and it has been a fun one. It's not too small or too fast so you can ride it anywhere. Get a four stroke bike unless you know how to work on them or your bike will be at the shop more than under you. Fours are low maintenance and a lot of them have many of the mx bike features. I have had several honda's xr's and crf's for my kids and they are indestructible. If you are buying a racing bike, I have always raced yamahas but I have owned one Suzuki RM and one Honda CR. Never owned a Kawasaki so I don't know about those. Good luck!
