That depends on what kind of car you will be working on. If you have SUV, you need something high – your typical 3 ton jack stands would not be tall enough for SUVs and some minivans. But they are good for most 4 door mid size sedans. So you would need combination of 3 tons, 4 tons, and 6 tons.
I use Torin and Big Red jack stands – they are in cheap side of the scale and made in China. Steels from China isn’t that great and the paint quality sucks so I will discontinue using them as soon as I see any rust.
I got couple of Craftsman 6 tons jack stands, but I don’t work on SUVs and don’t need to jack up the car that high for the most of the job. The only time I used them was to replace the clutch on BMW 5 series (Transmission was pretty big so you would to jack up the car pretty high)
I’ve seen some good ones made by AC Delco and Hein-Werner. If I had to start all over again, I would go with them (they do last long time) or Craftsman Professional 4 ton
I also have 2 5-ton screw jacks – I use them for general support (such as supporting engine while replacing timing belt). These things can hold the weight, but can also be adjusted by turning. I used to do this using floor jack, but they do loose pressure over time.