It is difficult to choose an ideal telescope as it depends on so many factors. I think you may be considering Deep Sky imaging, which has similar requirements to variable star photometry and comet imaging. While planetary imaging has different needs.
I would say good quality optics of a variety of designs can produce excellent deep sky images. If you want top quality results, then put quality before aperture within your budget.
A key point is ensuring you have a good quality mount that can robustly support the telescope and track well, or receive guider commands to correct for tracking errors. With smaller telescopes, such as small short focus refractors, you can get away with a much smaller and cheaper mount. As you go to larger telescopes and longer focal lengths, the cost of the mount will go up dramatically.
It is also important to have a focuser that can support the camera, as well as any filters or an off-axis guide camera if used.
For starting out with imaging I would recomend a short focus refractor. However, something like an 8-inch SCT on a sturdy mount is a great all round telescope. With available accessories that can be used for both deep sky and planetary imaging.
