If you are one of those fortunate to live in area without light pollution, you should think big when you think
telescope. Take it from me, someone trapped under the city lights, a
big telescope under light polluted skies will never reach its full potential and, to make matters worse, an area with a lot of light pollution is also an area that typically has a lot of other kinds of pollution. This means that sky transparency in the big city is never what it is in a rural area and sky transparency is almost as important for seeing the faint stuff as a dark sky. Bottom line - if you have a dark sky site, go for all the marbles. Get a big
telescope.
On the other hand, if you live in an urban area, keep portability in mind. You will, sooner or later, want to take your telescope to a dark sky site and if the telescope doesn't fit in your car or if it requires a lot of
dismantling to travel, you aren't going to get it done. That's a shame,
because you'll never know what your telescope can really do until you get it under a truly dark sky.