5 valve Yamaha reliability is in fact atrocious. However, all things considered a 690's combined issues will approach the amount of pain a failed valve on the Yamaha will bring. Between those 2, I'd take a 2nd hand KTM 500 and have none of the issues.
Wise words!
500/501(2016 model) is the 2017 way to go.
I have had lots of riding buddies with WR's and zero reliability issues. Both my son and myself has had 690's, and what shit they are. Everything of the cheapest.
Then again, we ride, we do not play around.
A failed valve does not matter whether it's on a Yamaha , Suzuki, KTM or Triumph, on any 4T a failed valve may bring disaster. If you worry about valves, buy a 2stroke.