Good morning, Ed;
All three of those brands of lenses have had some really good lenses, and, some ones that did not really quite make it also.
In the Tamron line, who can forget the first version of the SP 300mm f/2.8 LD IF telephoto lens, the Type 107B, where they forgot to include the small filter at the back of the lens in the optical design. Yes, that lens performed better without the "normal" filter in the holder than it did with it in place. The next year when they put out the Type 60B where the filter was included in the optical design, that lens did much better with the "normal" filter in place. Then there is the performance of the SP 90mm f/2.8 and the SP 180mm f/2.5 where you will go along way to find something that will outrun them in the OEM lenses.
The Sigma people have had a really wide ranging success level. There were a couple of lenses a few years back that produced a bad taste in the mouth of many photographers, but in recent times, there are a couple of their zoom lenses that are really good performers, such as the new 8-16mm f/4.5-5.6 that seems to be very well received in comparison with the earlier 10-20mm f/3.5 and f/4.5-5.6.
The Tokina people (a group of Nikon optical engineers who left Nippon Kogaku, or Nikon, to form their own lens company; sort of a true return to the original roots of Nippon Kogaku) have had some good lenses also, mainly in their ATX series.
All three of these companies have produced some good lenses, and also some that did not really make it, as mentioned. Of the three, the Sigma people probably have had to work the hardest to overcome their past reputation. Tamron has enjoyed a very good reputation as a third party lens manufacturer for years. The Tokina people may have had some difficulty with name recognition, although I am not really sure why.
Now. What do I have? Of those three, mainly Tamron with about 20 lenses. One of them is their new wonder lens, the 18-270mm f/4.5-6.3 lens for digital APS-C sensors. So far, I like it. There are also the SP 90mm f/2.8 Macro lens, the SP 300mm f/2.8 LD IF, and a couple of other well known performers. I started with them with due consideration to the Adaptall-2 mount system and its earlier incarnations, the Adaptall and the Adapt-A-Matic. I have only a couple of lens types where there are lenses from each of the manufacturers, but I do not yet have any really definitive data for making a dispassionate comparison. That might be an interesting task for this coming summer.
Please keep in mind that for any really meaningful comparison, there should be a reasonable size statistically valid sample population. I am not sure that I can make a truly rigorous testing of the lenses that will withstand the scrutiny of knowledgeable people.