There are pretty clear differences.
.ws is a cctld that was heavily marketed to mean "web site." Over the years .ws has generally cost $15 - $30 to renew. .xyz costs the same as .com or less $8 - $12 to renew.
.xyz is frankly easier to remember. And people are choosing to register .xyz at a time when there are '1,000' alternative ngtlds. Whereas back in the early 2000's when people were registering .ws domains, there were not as many alternatives available.
An additional note.. Over the last few months, I have noticed .xyz growing in interest both from end users, e.g: registration number, and also domain domain forums.
I hope .XYZ will come out as a long-term winner. Though it's impossible to say for sure with new releases coming later this year.