Seems like the 86-87 200x is the hot ticket right now as they are going for small fortunes on ebay!
My buds and i used to ride a big pack of 200x's only. From our experience the first gen bike was much tougher and more reliable, plus it could be made faster since there was alot more aftermarket upgrades available.
Our only problems with the 1st gen x's was carrier bearings went out once a yr. since we ride dunes mainly. the kicker was a pain in the rear and the rear brakes seemed to never work (none of us had rear brakes on any of ours) they are super tough and have great stock suspension when dialed in to your style and we all picked ours up for 500$ or less each
The 2nd gen x was a little faster and better looking but we had alot more issues w those. cracked frames, swingarm bolt seizures, kickstart gear problems, clutch problems, broken oil pumps, carrier bearings etc. the guy who bought the 2nd gen x sold it and switched back to first gen.
jumpn jon (far right in pic) switched from a 1st gen x to a 350x and quickly did not like the bike saying it had power but was too heavy to jump big gaps and he broke the frame, now he wants a 1st gen x again despite the power loss. reliability counts more if you ride hard!

Not sure why the 2nd gen x is in demand? is it the short 2yr run? not sayn there bad bikes, either way we'd ride 1st gens anyday over the 2nd gen