Hi incognito,
They both make mattresses that use high quality materials and there are no lower quality materials or weak links in the mattresses made by either company.
Any other differences would depend on the specific mattresses you are comparing because the specifics of a mattress and how well they “match” the parts of your personal value equation that are most important to you are more important than the name of the company that makes it. There is more about the most important parts of the “value” of a mattress purchase in post #13 here.
There are pros and cons either way. Many of the latex-pedic mattresses are two sided which generally do best with gluing while many of the mattresses that Plushbeds make are component latex mattresses that have the ability to exchange a layer so gluing them would remove this advantage. There is more about the pros and cons of two sided mattresses in post #3 here and there is more about the pros and cons of glued vs unglued layers and zip covers vs tape edged covers in post #2 here and the posts it links to.
Phoenix