Which is better - short or long tubes?

Laboratory tests have demonstrated that shorter tubing provides a better acoustic response. In reality, most people do not have the hearing acuity to detect any performance impact from changes in tubing length unless there is a dramatic change in that length. In fact, the acoustic transmission of lower frequencies, with their longer wavelength, benefit slightly from increases in tubing length. Longer tubing tends to make the scope more convenient to use, but also adds a bit to its weight. Bottom line - tubing length is generally a matter of personal preference.