Posted 10 September 2017 - 02:41 PM
Let's take a look at three of the four brands you mentioned when it comes to buying a 127mm Maksutov:
Celestron offers the Nexstar SLT127-- a 127mm Mak on its SLT mount
https://www.celestro...rized-telescope
Celestron sells it for $549, but you can find it for $100 less (sometime even cheaper) if you shop around.
Orion offers its Apex 127 on its Star Seeker IV mount:
http://www.telescope...L4aAu4gEALw_wcB
The Orion scope and mount sells for $699
The also sell a spotting scope version for $369 that includes the OTA and 45-degree diagonal.
And Skywatcher sells a 127mm Mak OTA:
http://agenaastro.co...WsaAgQ1EALw_wcB
Prices at US vendors run $399-$450
Which scope gives the best views? Look at the pictures carefully. The only apparent difference between the OTAs is paint. All three OTAs come from the same factory in China. I suppose it is possible that one manufacturer may pay extra for better coatings or quality control, but given that none of them are making any such claim, it's doubtful. At any rate, I suspect there may be more variance from one OTA to another in any given brand than there is between the average OTA from brand to brand.
Which is the best value? If you want a scope and goto mount, the Celestron packs a heck of a value. The Orion package gives you a better mount, but you pay rather a lot for it. Is the Star Seeker IV worth the extra $250? It comes with two eyepieces of indeterminate quality (Orion doesn't sell them separately), while the Celestron only has one. The real value comes the better mount. If your funds are limited, it's hard to beat the Nexstar 127, but if stability is paramount to you, you might consider the Star Seeker to be well worth its premium.
But what if you only want an OTA? The Skywatcher comes with a 2" star diagonal (which some people consider a dubious feature for a 127mm Mak). The Orion comes with a 1.25" 45-degree diagonal for terrestrial use, which is of little value to you for astronomy. If you want a 1.25" star diagonal with your OTA, the best value may be to buy the Celestron and sell the mount!
FWIW, I own the Orion Apex OTA, which I bought used to use on a Celestron 4/5SE mount. I ended up opting for a C5, which I find I prefer over the Mak. The Orion Mak will likely be up for sale in the near future,
Anyway, I hope that helps to illustrate why brand ranking really wouldn't be of much help. As Jon said above, you pretty much get what you pay for. Occasionally, you'll find a product that is truly disruptive, but then the market adjusts. And almost always, if a deal seems to be too good to be true, it is.