I'd say .online is looking great considering it's only 10 months into General Availability.
.xyz GA began Jun 2014
.link Apr 2014
.red Apr 2014
.club May 2014
.bid Jun 2014
.want Jun 2014
.top Nov 2014
.science Feb 2015
.site July 2015
.win Aug 2015
.online Aug 2015
Personally I consider .online as a Top 2 new-gtld since "online" is already a desired keyword, and it's just so wonderfully generic. The only other one I really like is .club (and to be clear, I don't think I own a single .club as of now... oops).
Forget xyz, it's never going to catch on in Real Life. Neither will top, wang, win, site, vip, link, bid, xin, science, red, ren, click, party, loan, date, website, space, etc. Some will have a handful of success stories, but none of the above will ever be "popular" with domainers or widely used for development. That's IMHO where .online and .club will stand apart a couple years from now when the dust begins to settle.