Dianas are cherished because they are no longer manufactured and are now quite unusual (and becoming rarer) vintage toy cameras.
Holgas on the other hand can still be bought brand new for about 25 euro. There is a very large Holga community around the world. There are two versions of the Holga, the original with a plastic lens and the Woca with a glass lens. They are very popular among lomographers who prize the vignetting and light leaks.