I'm 5'8" 140 lbs, and currently have a ktm 125 sx for mx. I would like a trail/dune bike to go with my friends because apparently mx is too cool for them haha. But I'm having trouble deciding on a bike. Right now I'm trying to decide between a KX 500, a KX 250, or a KDX 220. Thoughts on this? I'm open to other brands too, I just don't want 5 different people telling me to buy 5 different brands of bikes. Feedback is greatly appreciated.

I think a 500 would be a lot of bike for trails, with that bigger motor will come extra weight. The kx250 would be nice and then is the kdx their dual sport bike?

Trail or Dune bike hun? Two very different disciplines! That being said, i love my 04 kx500 for both. Yes, i ride single track with it. It is a heavy bike, but has abundant low end power when you need it.  Given your size , though , the kx250 would be a better fit, due to weight. I would recommend the kdx200/220 if you weren't going to the dunes, although you would get away with it given your light weight. The kdx is a good woods/trail bike , but has soft suspension.It is NOT a dual sport, although in SOME states it can be licensed as such. If you are stuck on kawasaki 2t's there is one thing you might take into consideration, most kawi  2t's require the cases to be split to replace the crank seals. Why do you care? Cause you are going to be buying USED. Leaking crank seals on a 2t can =GRENADE, but at very least will give you eradic unpredictable idle/power. I love my kx500, but am soured on kx 2t's, due to the aformentioned flaw. I got the solution, atleast for the weight, KX500 af conversion , based on an 07/08 250f chassis, would go maybe 235-240 lb. I know , a little over the top, you won't go wrong with a kx250, as long as you don't mind splitting cases........

i think at the dunes you would have a blast on the 500!!  trails maybe not so much, but it can be done.  check out kxriders.com.  lots of guys over there running KX500s on the trails.  I had an 03 kx500 that was a great desert beast.  on the trails the engine was great, but the bike did have a long feel to it.  If i still had it I would look into a hydro clutch.  I tried different levers, and different cable routing, but after a few hours of riding my fingers i use on the clutch were sore.  another popular solution was to lengthen the clutch actuator at the case, but i didnt get that far.   it had a pretty stiff clutch pull. the trails i was on were not the tightest or most technical but i was using the clutch a lot to control that monster motor.

never been on a kx250. but you cant go wrong with a 250 2 stroke on the dunes or in the trails, especially at your weight.  500 would be overkill.  but there is nothing like that big bore 2 stroke power!

I was being on the conservative side with my other post, not knowing the skill level of the OP. I would love to see a new guy on a 500 smoker as long as it doesn't kill him! They have always had a bad rap as being UNridable.....whatever. Ride a gear high and they will  tractor quite well , ride them like a 250 and you will be disappointed or hurt. The kx500 has a pretty sweet all around power band, pulls low and pulls fairly high for a 500. I guess the best thing to do is to ride it and decide  for yourself. On a side note the old kx500 has a fairly low seat height for a full size bike , which is a plus for trail riding.

Really, you can't go wrong with a 250. They do everything pretty well