Good quality refractors are always more expensive than reflectors because the manufacturing process is longer and more complex, and the types of exotic glass used cost more.
There are many different opinions about which is "better": but it is always true that, all else being equal, larger apertures gather more light and give brighter images at the same magnification. A larger aperture will potentially give finer resolution as well: although this will not generally be noticed in low power images. For visual use you will definitely see fainter objects in a 250mm scope vs a 100mm. For AP use it wont make much difference as you can take longer images, gathering more light to compensate for the smaller aperture.
A good refractor will generally give cleaner star images and better contrast than a reflector, due to the central obstruction of the secondary mirror in the reflector. The reflector will also show "spiked" stars because of the vanes holding the secondary mirror. This means the refractor may give a more aesthetically "pleasing" visual image, and for this reason many people are refractor afficionados (myself included).
For AP, both should give you great images but the lighter of the scopes may perform better as the mount isn't straining as much to push it around. Generally, if you want to do AP, you don't want to go much above 50% of the mount's rated capacity.
The ED100 is I believe f9, while the 250 is f4.8 or 6 (seem to be different ones out there). The faster the focal ratio, the less time you need to capture an image: so the 250 would win easily on that score.
However, I will leave it to the AP experts to comment further.
All the best,
Dean
PS: I was writing this while the other guys posted: but I agree with their comments.
