When it comes right down to it this class of telescope may be all that you will ever require. These scopes are still small enough to take just about anywhere, are in general easy to set up, and will provide you with decades worth of objects to observe. They are also relatively inexpensive. With this class of instrument all of the Messiers are within your grasp along with much of the NGC catalog. Visible are thousands of galaxies and hundreds of diffuse nebulae, planetary nebulae and star clusters.
Many globular clusters resolve into myriad stars.
The brightest quasar, 3C 273, is visible in a 6-inch. This is the workhorse class of telescopes. They will do everything that the Messier class will, but more so. More galaxies and faint nebulae will be within their reach, and some objects will reveal a bit more detail. They are, however, less portable and more expensive.