ive got a drz400
comparatively to the wr250r
Pros:
>faster, more powerful, higher top speed
>larger displacement, less highly strung
>ability to easily increase with widely available big bore, cam and carb kits
>exhaust can be changed without needing an expensive ecu swap
Cons:
>less reliable (subjective, but efi makes it more reliable)
>heavier
>extremely old engine/carb design which really needs modification to pick up
Personally I own a 2011 drz400sm which i love and got in January. At the moment it's burning oil on start up (i think valve stem seals) and im constantly worried that im destroying it by running lean because im running the stock jetting with effectively a straight pipe. Furthermore, the pipe isn't made for my bike and doesn't really fit properly.
I've got an enduro set up for it and love going offroad, its mad fun but for street riding, sm wheels are a must. On my enduro rims I have proper AC10 (DOT legal) offroad tyres, and pilot power 3 street tyres on the sm rims. Id say that ultimately, if you ride offroad in mud, having dual sport (road usable) tyres, its basically worthless in both situations. However, I have never used any as I have two sets of rims.
Overall, the drz400 is a great bike for all occasions, but not an excellent bike at anything. The fuel tank is too small, the thing has no wind/weather protection, and it isn't overly happy on the freeway at anything over 110. Top speed is about 160 indicated so probably about 145 (on sm). Its fast 0-60kmph and is decent 60-100kmph, but anything over that youre getting very quickly left behind. If our mates run sportsbikes, you'll be left behind anywhere except tight twisties. Similarly offroad, if you have mates with proper mx/enduro bikes, you'll be quickly left behind because the drz is too heavy.
If its your first bike, go for it. If you want a low maintenance dirt bike, which is fun its decent.