[Wavytone]

The right choice depends on how deep your pockets are and what aperture/focal length you are after, the size and pixel spacing of the sensor you are aiming to cover.

For a smallish aperture the Vixen 4-element petzval refractor is hard to beat, forget small reflectors.

For something in the range 100-200mm aperture my choice would be a Maksutov-Newtonian, several to choose from; not an RC or simple Newtonian. Next best is a 200mm Newtonian with field flattener and coma corrector; cheap and OK for a small sensor.

If you want 300mm aperture and can afford it, a Riccardi-Honders is the ducks nuts especially if you have huge sensor. Failing that, a Ritchey-Chretien cassegrain at f/8 or f/9 (GSO) or the scopes from Vixen with sub-aperture correctors at the secondary mirror. Next best, a Newtonian with coma corrector and field flattener.

Past 350mm aperture the Ritchey-Chretien cassegrain is just about the only solution available to amateurs as the cost of a large full-aperture corrector is quite simply prohibitive.