Unless jack stands are thick milled or rolled or formed or forged metal I don't trust them, as poor castings and thin metal can fail 'catastrophically'. Plastic ramps can be durable, but they can also exhibit porosity and fail badly, and chemical resistance might be a problem (what did you spill on the them the last time you used them ?)
I'm still using wooden blocks, and while I'll use my jack stands once in awhile I don't trust them and won't crawl under the car when they're the only thing holding the car up. This last summer we had a huge piece of machinery fall off of a truck and block I84 for awhile. The company that managed to lift back on a truck seemed to in part use lots of big wooden blocks.