I am a strong proponent of 125's. Of course my first real race bike was a 125, a few years before modern four-strokes were even available, so I have fond memories of the two-stroke days. Nevertheless, I do believe that if you can ride a 125 well, then you can ride just about any motocross bike. People who have only ridden four-strokes tend toward minimal clutch use because they have never had to fight to get the most out of the motor. Not that this is bad, its just a different technique for a different era of riding.
While 125's are a heck of a lot of fun, they also require a much different type of fitness than four-strokes. Where for 450s and 250Fs, muscle strength is crucial, a 125 or even 250 two-stroke rider had better be in great cardiovascular shape if they want to compete with the thumpers.