It depends on what you plan to do with the scope. For general viewing I'd go with the 9.25" Celestron. It has enough light grasp for most DSO's and consistently the best optics of the bunch. It is light enough it is easy for nearly anyone to transport and set up.

If you want it for long exposure deep sky photography then I'd go with a 8" or 10" GPS if the setup is to be used portable. The 10" is a lot heavier than the 9.25" Celestron but GPS scopes have a much better mount for long term tracking mainly due to this mass. The 10" is about as large as one person can easily set up in the field. Most prefer the lighter weight of the 8" however. It's about the same as the 9.25" Celestron.

The likely reason you see large GPS scopes on the market is many think deep sky photography is much easier than it is and don't expect the scope to be too heavy for them. Put the two together and you see them on the market a lot. I've seen several members of our club do this very thing. There was nothing wrong with the scope, they just didn't have the back for it. I certainly don't and even 40 year younger I'd have had trouble with a 12". That said I have a 14" LX200R but on a Paramount not the GPS mount. It takes two of us to demount or remount and the other guy is a young ox of a guy. But since it is a permanent setup this is only an annual chore when I regrease the gears. It's optics are excellent, far better than the early model C14 at Hyde Memorial Observatory but equal to today's C14 scopes. Putting a 12" GPS atop a wedge in the dark is a very difficult task. One I'd never want to try at any age without help.

Of the SCTs in our club I'd rate the modern version of both scopes about equal for optical quality except for the 9.25". It stands out from the rest. As a result it is getting to be the dominant new SCT being bought by our members. Keep in mind comparing one sample of each doesn't tell you much as both companies are known to put out the occasional unusually good or bad scope. Both sell scopes with and without enhanced coatings and both have increased optical quality in recent years so if comparing one of 3 years old to one of 12 would likely show the older to be inferior.

Everyone seems to have a different opinion about telescopes, this is just mine. It may not apply to your situation at all.

Rick