All and none. Depends on what lens you want and are comfortable with. normally for portraits people will use primes often 50mm(30/35 for crop) and 85mm. After you have narrowed down the focal length you want than it's time to google for reviews and also your budget.
There isn't one brand that only has damn good portrait lenses.
For Nikon, most beginners would consider the 50mm f/1.8D/G, and the next step up is 50mm f1.4D/G or even the 50mm f1.2 (manual focus), if you are into manual focusing.
Or if you want something wider, you would want to try the 35mm f1.8G, as mentioned by some of us here.
The next step up could be a telephoto zoom lens such as 70-200mm f2.8, or the 85mm f1.4/8D/G. Let's not forget the 105mm f2 or 135mm f2.
To be honest, the kit lens can take nice portraits too... You might have realised that most of the lenses mentioned are not in the wide angle range... because you might want to have as little distortion as possble while shooting portraits, of course, you could still take portraits with wide angle lenses.
Moving to Sigma, they are rather known for their 30mm f1.4, 50mm f1.4 and 85mm f1.4, with the 85mm f1.4 being cheaper than the Nikon G version. Or their 70-200mm f2.8 is also for those on a budget. Do note that their QC isn't that consistent as compared to Nikon.
For Tamron, the more well-known lenses would be 17-50mm f2.8 on DX or 28-75mm f2.8 on FX.
I have not heard of any portrait-oriented lens from Tokina... since they are known for their 11-16mm f2.8, and now probably the 16-28mm f2.8.
All these lenses are all good.. like I said, different brands offer different lenses, for different segments of consumers. Even the kit lens can take portraits, all these lenses can definitely get the job done.