[mc32]

Probably one of the corporate ones like .xyz, .amazon, .bananarepublic, etc.

[jobigoud]

"As of June 2016, .xyz was the fourth most registered global top-level domain (gTLD) name on the Internet, after .com, .net, and .org." -- Wikipedia.

[wereHamster]

.xyz is pretty easy to get, it doesn't even cost that much, it's affordable even for individuals

[panzerklein]

.xyz is easy to get. Also cheap.

[adventured]

I believe anyone can register the .xyz domains. They're typically on sale for $0.99 on GoDaddy for the first year, so there seems to be a lot of junk, volume registrations using it.

[mc32]

My bad, my main point is that likely the most restrictive would be one of the corporate/private TLDs that are for internal use mainly. .xyz was a bad example. Maybe better is .bananarepublic

[CydeWeys]

There's literally hundreds of new gTLDs like this that only have the one required nic.tld on them and nothing else (because they haven't launched yet and might never). My team runs a couple dozen of these.

For comparison's sake, we should probably restrict ourselves to legacy gTLDs, ccTLDs, and open, launched new gTLDs.

[lathiat]

.duck, sadly.