Your First Telescope:
This should be small, efficient and rewarding. Nothing under 10cm or 4” is a useful learning scope and a reflecting telescope is preferable. Cheap refractors of this size tend to come with flimsy mountings, minuscule finder scopes and poor eyepieces. While small refractors are great on the Moon and the major planets they have great limitations on most deep sky objects. Interestingly, many experienced observers still keep a telescope of about 10cm and return to it after they have traveled the full gamut of telescopic adventures, no doubt as advancing age makes lifting and setting up a chore. Such a machine can reach all Messier objects and much more.
Your Last Telescope:
This is much more crucial, as it is the machine that you will use the very most and help expand your knowledge of the skies as the years progress. While I have looked through a wide range of telescopes and experienced the sheer joy of deep sky objects in Ultra Large scopes, realistically the larger the scope the less use it gets. After much pondering I have come up with the magic size of a 25cm(10”) objective as the best value for money, best mobility, optimum user friendship and, surprisingly, capable of reaching enough major deep sky objects to fill a lifetime of observing.
What about electronic assisted Telescopes?
Great, if you can afford them and if they make life easier, but does the improved image of the Eight Burst Nebula appear that much better in the expensive machine and can you still point it out to friends in the field when you have a computing glitch?