.online
Hands down.
Many reasons why I say this, but all you really need to do is go to
ntldstats.com and click each of the Top 10 extensions. All show abnormal growth patterns, except for -- you guessed it --
.online. No shenanigans here, just steady growth from the start.
Let's also keep in mind that out of 1,197 new gTLD's,
.online is the
#1 most represented in the Alexa Top Million. That's pretty impressive considering that it's been largely ignored by domainers due to a belief that it's "too long". Or perhaps more domainers are indeed scooping up .online than we realize. . .
Despite the lack of current
domainer activity, sales are nonetheless occurring. A small portion of those (24 as of now) have been listed at
namebio.
Overall, in my opinion, .online is at minimum a Top 3 nGTLD -- and not at all priced like it. At present it is VERY cheap to acquire some VERY nice keywords and LLL. Registrations are only $1.06 right now at Namecheap.