The last few years has seen a new commercial telescope available on the market - the Dobsonian. Little or no maintenance. Excellent for lunar, planetary and binary star observing especially in larger apertures. Good for distant terrestrial viewing. High contract images with no secondary mirror or diagonal obstruction.
Colour correction is good in achromatic designs and excellent in apochromatic and fluorite designs.
Sealed optical tube reduces imagine degrading air currents and protects optics. Objective lens is permanently mounted and aligned. Heavier, longer and bulkier than equivalent aperture Newtonians and catadioptrics. The cost and bulk factors limit the practical useful maximum size objective to small apertures. Less suited for viewing small and faint deep sky objects such as distant galaxies and nebulae because of practical aperture limitations.