If you want the real deal, the original genetics then you have one option. Mr. Nice Black Widow, as has been mentioned. All others are knockoffs, different breeder’s own version with differing genetics from not only the original but also all the others.
 
If you are only going to pick from the three you mentioned I would pick Seedsman Seeds White Widow.
Nirvana has lousy quality control because they have other people, lets call them contractors, make their seeds and they differ in quality and some do not even turn out to be what they are sold as because the person who supplied them to Nirvana claimed them to be a bean they could charge more for or mixed in some cheaper genetics with the better ones so they could then make more profit by there supposedly being more of the higher dollar beans than there actually are.
 
The only G13 Labs gear I have grown has been several different types of freebies given out with purchases from Attitude and while White Widow was not one of them overall I have not been impressed with G13 Labs gear so I would pass on them.
 
I have grown Seedsman Seeds White Widow and I will not say it compares with the original White Widow that was renamed Black Widow I was still fairly impressed. The growth was vigorous right from the start, the nodal spacing was very tight, it created many, many but sites and production was impressive.
 
It was mentioned that Seedsman Seeds is predominantly sativa and that is correct but at least in my case the plants did now have a sativa dominant growth pattern or flowering length period. They were not tall and lanky and lower in production or took long to flower. The pack the beans came in said 8 to 9 weeks flowering time. (Of course those are only general time periods, basically estimates that can and will vary due to different setups and growing conditions) As a comparison the original White Widow/Black Widow says 8 to 10 weeks so regardless of the difference in the percentages of sativa the general overall flowering time in each is not all that much different. The difference with the Seedsman Seeds White Widow is that it only resulted in a slight bit more of an increased head high than some other versions of White Widow will give you.