Thinking of buying this telescope for astrophotography?

Both of these are excellent telescopes, but the SkyQuest XT10 is on a Dobsonian mount which is completely manual and has no motor drive, so is unsuitable for any sort of astrophotography beyond snapshots of the Moon and planets. It has a computerized object locator, but no motors to drive it, so that you must centre and track objects by hand. The 120mm has very good optics and is mounted on a solid equatorial mount with an autoguider port, which is something you should consider down the road. But it is definitely more suitable for astrophotography than the 10" Dob. It has an accurate motor drive and slow motion controls on both axes, needed for guiding.