You really need to decide what you want to image, and a focal length you'd like to image at. There is simply no point looking at every scope there is in the market and trying to pick the "best" one.
Decide if you like wider field shots (400~700mm F/L) moderate (700~1300mm) moderate long (1300~1700mm) or long (1700~3000mm) Decide simply by looking through the forums at images, take note of the ones that strike you the most, and take note of the focal length...
Bare in mind that 1700~3000mm is extreme, will take either an incredibly stead fast resolve or a really expensive mount to pull off great images in this range..
Once you've chosen your desired focal length, you'll notice your list of possible scopes has become much more manageable. From there look at their pro's and cons, consider the camera you will be using with the scop, and determine what your needs are in terms of F/ ratio..
This is pretty much the process I go through when picking a scope..
General rules of thumb. anything with glass in the optical system is either going to be really expensive, or have some form of aberration, this can be true for purely reflective systems too. but often a "cheap" APO telescope will exhibit less than perfect colour correction.. Generally speaking, If I were looking to spend less than $1000 on an imaging telescope I would steer clear of refractors.. Thats not to say there are no good refractors sub $1000, just to say they are not considered common... Reflective systems under a grand you've got newtonians which deliver sharp images when collimated properly, maintainance can be a pain though, as collimation will generally go out every time you physically move the telescope, cassegrains (maks, SCT, RC's) These vary in quality, some mak casses are really nice, some are not, SCT's arent really an imagers dream scope due to the moving primary mirror, rather large spot size and a sealed tube which makes them hard to cool, RC's are generally out of the price range, however the 6" GSO RC is 1390 or there abouts I think.. However I dont kow anyone who has bought a 6" one yet, so there is no testing done, also they are an F/9 system, meaning that you'll have to be taking some long exposures to get serious data...
Mak Newts do make great imaging scopes when set up correctly...
I know there is a 10" F/3.5 Meade Schmidt Newtonian for sale on the forums at the moment, which would make a FINE imaging scope.. Collimation on these is apparently fairly tricky however, the results would be stunning with a large imaging sensor like a DSLR..
There are simply too many options out there to ask the broad question "what should I buy?" You could follow the route I've gone, and try to own one of everything at one stage or another to find out for yourself what works best, Or you could be smart with your money, narrow down your search perameters and find what is going to be the best for what you want to do before spending truckloads of money on numerous telescopes!!
If I had my way, I'd own a 10" newt, a 14" SCT, an 80~100mm fluorite triplet APO, maybe one of those Intes Mak Newts and an RC with a mount big enough to carry them all at once..
