Where I live, it's great for riding most of the year, but when the rainy season comes it's mud everywhere. My question is, is it better to have a D Tracker with a set of knobblies for the wet season, or a KLX250 with a set of road tyres for the dry season ?
The D-Tracker and the KLX are the same bike its just the D-Tracker has smaller rims not sure if you can get knobbys for the D-Tracker rims so just buy a set of KLX rims to stick on it when you want ... or buy KLX 250 and buy a set of D-Tracker rims for it.
I just have a knobby on the back and a road trail tyre on the front of my KLX250 all the time but thats what i like. ;-)
Assuming you keep the same rims and just change the tires, I would go for KLX as the bigger wheels are better on dirt. Also the dirt wheel are not that bad for "good" road. I have been driving 18000km on KLX with motorcross rubber on all kind of dirt and mud and black (asphalt) road (including Udon - Luang Prabang - Udon 100% on asphalt) and it is actually quite ok.