What is a good focal length for DSO I found two telescopes that i'd like to buy, but one has 900mm focal length ((Skywatcher Newton 114/900 EQ1)) and the other has 500mm focal length ((National Geographic Dobson N 114/500)).
My questions are:

What is the &quot;recommended&quot; focal length for observing deep sky?
Are there better telescopes in the same price range?
I don't think there is a &quot;recommended&quot; FL for DSO observation. If you only observe visually, the eyepieces you use are just as important und the magnification depends on them. If you are concerned about the field-of-view you will get from these telescopes, I recommend checking out FOV calculator tools such as astronomy.tools. There you can enter your telescope and eyepiece information and show the FOV compared to a deep sky object of your choice.
I personally have been very happy with Skywatcher telescopes (I own an Esprit 100ED Triplet and a 200/1000 Newtonian), however I never really tested them visually as I only use them for imaging.