Indeed the question as posed is unanswerable.
Telescopes are used to take images in two basic ways (not counting spectroscopy):
1. To image faint objects
2. To image fine detail
(3. Some combination of these)
Aperture allows you to resolve detail, but focal length allows you to image the resolved detail with a detector. Aperture also allows you to image faint stars, but the imaging of faint extended objects depends inversely on focal ratio. Width of field, with a given detector, depends inversely on focal length. If you wish to image the combination of faint stars, faint extended objects, and detail, you require a large aperture at a low focal ratio. If you wish to image wide fields you need a short focal length, but unless you have a large aperture and hence a low focal ratio as well, your detection of faint objects and your resolution will be limited. But there is a limit to how low focal ratio can go without optical problems, so for the widest fields, very small telescopes are needed, which are limited in both resolution and limiting magnitude.
This is all before one gets into considerations of mounts and drives.
So what is ‘a good telescope for astrophotography’ depends on what exactly you are trying to achieve.