Having ridden a late model XR250 and currently owning a 99 KDX 200, I offer the following. Both are reliable and the after market up grade possibilities are endless. However, the KDX is lighter and more powerful to begin with, thus requiring fewer, less costly modifications to acheive a higher state of performance. The engine is forgiving, and with a few simple, low cost mods, can offer the rider more then enough power for any situation, be it desert or single track. The XR can achieve similar performance levels, but the cost is greater because the modifications required are more involved: big bore kits, after market carbs, etc..In order to go fast, both must be wrung out, but they can take it. Also, starting the KDX, be it hot or cold, isn't as frustrating. All that said, either one is a great bike, representative of an era when the manufacturers realized what most people want and need from a trail bike. The late model XR's are pure trail bike, that offer good performance for that application. The KDX reaches a more middle ground approach in that they too are friendly trail bikes that can be raced competively in the lower skill classes with but a few modifications.