Like anything else, it depends on what you want to do with the scope. For Planets I would definitely prefer the ETX 125. Is it a current model or an old one?
The current ETX 125 Observer sells for about $700 and is an F15 127 mm/5" GoTo Mak on a fork mount. Very nice optics and well suited for planets, solar, splitting double stars and other medium to high mag applications.
If it is an older ETX 125 AT ( I have one) is still an F15 127 mm/5" Mak. Older models were on a fork mount but were not GoTo. Later models could have the GoTo hand set added and finally the included the GoTo handset as standard. I have the 125 AT with the GoTo handset.
The GoTo mount is dedicated to that optical tube. You can't slip other scopes onto the Goto mount. However you can defork the ETX optical tube, put a dove tail on it and use it on other mounts. I have done that. It is not quick so you would not remove it and swap to a different mount during an observing session.
If the mount works and the optics are intact it is a nice scope. The tripod is very robust. I would prefer this one.
I presume this is the Orion. The Orion is an F10 achromat on a manual Equatorial mount. I don't know that mount but I always ask if people know how to use an equatorial mount. Some love them and some find them confusing. https://www.amazon.c...r/dp/B0000XMSKC
An F10 achromat is not bad for planets. It will show come chromatic aberration, but I would expect at F10 that it won't be too bad. Should work fine for planets and the like. Because of the shorter focal length it has the potential to present a wider field of view for other DSOs, but I would prefer the 5" Mak for planets.
Edited by aeajr, 18 January 2020 - 08:55 PM.