Go Jacks versus cheap cr*p
At the risk of being shot down for price. I bit the bullet and bought Go-Jacks, I only have these, so cannot comment on others, but I could not be more happy with the ones I have.
We use these at the office and they are the best. But they are nearly $500 for a set of 2. We have no problems with cars coming off them. and you can use them without a floor jack (a HUGE benefit)
The only 3 drawbacks I can see is they might temporarily "flat spot" the tires if you leave a car on them for a long period of time, they stick out just a little which means you can't get your cars packed it as tight, and I can't afford them. I use a cheap sh*t set of imported dolly with curved beds from HF, but they don't "flat-spot" the tire belts. They don't roll as easily as the good stuff, but I can leave an old car on one for an entire winter and in the spring the tires are still round. At the recent Jag meeting, we had a silent auction and a set of gojacks went for $250. I would have gotten them had I not been stuck in stupid Boston traffic.
Another solution is to buy smaller, lighter cars, so the tires can't flat-spot and even the cheap rollers work well enough.