A KDX is a great first bike choice. As you get better, you can make it better and faster. Get the suspesion done before you start on it,9 stiffer springs , Race Tech valve package), to make it work way better.
My KDX was a bike that never did anything scary, very user friendly. The only thing is it's like the XR's, old technolgy, feeling, but the worse the trail is the more it shines!
I have a ATK 250 now and love it.
It's super user friendly, smooth power delivery, less maintenance than my ol' KDX, the suspension is 1000 times better. Plus it feels like I'm riding a 125 cuz it so light, about a ton lighter feeling than my KDX.
Before I'd buy a KDX, I take a serious look at ATK.
The dealer network my be a tad thin, but you can PHONE the guy at the factory who built your bike, order the parts, (If a dealer is more than 50 miles from you), and they'll ship the parts to you!
I had a ATK 125 last 2 years and this ATK 250 this year and short of basic maintenance stuff, (Piston/ring once a year), they never broke anything! Never let me down.
It's got like all top shelf stuff on it, (better than KTM!)
Joe