It all really depends on what you want to do – but short focal length refractors are a popular starting point for imaging. The wider field of view will be more forgiving of tracking errors, and many are a good match to a DSLR.
As Paul says – a good tracking mount is essential. And GOTO is useful. If you can get good 30s exposures which you can stack you will find a huge range of potential targets in reach.
Callum