I agree that the bigger and sturdier the jack stands, the better off you are, safety wise. But sometimes the bigger jack stands require you to jack up the car really high in order to get them underneath it, which stresses out the wheel bearings on the opposite side. So...you have to then jack up both sides of the front or back and put the jack stands underneath each side. Sometimes you just need to do a quick repair, and the smaller jack stands come in handy. I use 3 ton stands for that.
I have been using floor jacks, bottle jacks, and jack stands alot lately (car repairs, motorcycle upgrades etc) and I have found that it's much easier when you have a selection depending on what you're doing. So, a small inexpensive 2 1/2 ton floor jack like the Wal-Mart or Sears ones, a big 5 or 6 ton floor jack, some small jack stands and some big ones, a $10 2 ton sears bottle jack, and some decent wheel chocks are what I'd recommend. This doesn't add up to much money, the only expensive thing is the big floor jack. I have some ramps too, but honestly, they hardly ever get used. You can't take the wheels off with them, and they're always in the way when your under the car. Occasionally they come in handy.
Also, when working on a car with a wheel removed and the car on a jack or jack stand, I always put the removed wheel under the frame rail, just as a backup precaution. If the jack slips, at least the car won't go all the way down with part of you under it. You might ruin the wheel, but better that than your hand or arm. hth
Oh, one more thing, make sure the floor jacks have a built in carrying handle, and are the kind that raise with one stroke before contacting the car.