The XR is a great bike for most riders. The suspension does need some work, but the bike is low maintenance and will run nearly forever. With some suspension work a good rider can go quite fast on one.
The WR is closer to being a race bike. Better suspension and more power but requires more maintenance. Expect to do engine rebuilds more often than the XR. Thats not saying the WR is a bad bike. I feel it is probably the most reliable modern 250f on the market. Yes it has Ti valves like the YZF.