I have left the original text of my web page unchanged, however, it is now a link to this page. But note the word, alternative . Now, there are some issues to be considered with your choice of observing instrument. A longer focal ratio will be more tolerant of good eyepieces, as opposed to excellent eyepieces. With a good Barlow Lens, proper choice of eyepiece focal lengths can effectively double the number of oculars an observer has to choose from.
Collimation is important for good imaging, and critical for planetary observations.
Alan pointed out that shorter focal-ratio newtonians can be more difficult to keep collimated. My experience as an SCT user is basically collimation-free. Another friend suggested that I check against a fourth magnitude star. Contrast is important for planetary observers. It can be important for observing galaxies, as well as emission, planetary and reflection nebulae.