Hi lightsout,
As you can see in post #1 here and the information, steps, and guidelines it links to … Sealy is one of the major manufacturers I would avoid in terms of the quality and value of their mattresses.
On the other hand … the Ultimate Dreams is a member of this site which means that I believe they are among the best quality/value in the country.
For me the choice in terms of quality/value between the two mattresses you listed would be easy because the Sealy is one of the mattresses I would exclude from consideration right off the top.
You can see a few more comments and an analysis of the Sealy Optimum lineup in post #48 here.
Phoenix