Hi Joan237,
Post #13 here has more information about the most important parts of the “value” of a mattress purchase that can help you decide which one would be better value to you.
Since your mattress is for a guest room and not for someone in particular then PPP wouldn’t be relevant because there isn’t a particular person that will be sleeping on the mattress.
That means that you would need to compare them based on the quality of the materials along with the other parts of your personal value equation that are most important to you.
This seems to be the Novaform memory foam mattress here which uses 1.5" of 3 lb memory foam and 2" of 1.5 lb polyfoam which are both lower quality materials. These would normally be a weak link in a mattress although in this price range they would be an “OK” choice because they will only be used less frequently if they are a guest mattress so durability may be less important.
Since you are buying from Costco you won’t be able to count on the guidance of the customer service there to help you make the best firmness choice for your guests so it will really be a roll of the dice (see post #4 here about buying from Costco). The only good news in buying from Costco is that you get a free roll of the dice because they have a great return policy so if the mattress doesn’t seem to be a reasonable firmness choice based on your own “best judgement” then you can return it.
These specs are also somewhat incomplete and don’t include the thickness or order of the layers but for a mattress in this price range they are fine in terms of quality/density and there wouldn’t be any obvious weak links in this mattress although I don’t know how it will feel for your guests. The Morgedal also comes in a firm and medium firm version (see page 8 here and post #61 here) and I would probably choose the medium firm if you decide on this mattress because it would be a better match for a wider range of guests “on average”. This uses higher quality and more durable materials than the Costco Novaform.
Phoenix