Re experience with Traveller:
I got the original box in 1977 and have played it on and off ever since. I didn't add the new stuff to my game because I had what I needed to get everything I wanted from those first three books. I changed what I wanted to, and added everything I needed. There's plenty of it. I played the game with many different groups over the years. I avoided the new stuff because I didn't like how it changed Traveller WRT how I played it.
Now I'm able to take a different attitude toward the material, partially because of the changes in how I play but largely because I'm willing to take what I want and ignore the rest without feeling like I'm doing it wrong.
Re the argument being about the "best" version of Traveller:
The sooner you get over this the happier you'll be, Ty. There is no "best" version. Of Traveller, of RPG, of art, of story, of song.
Different things appeal to different people at different times for different reasons. That's not what this is about at all. I read this as being about why is it worth it to those of us who like it and buy it. That means the discussion is about whether the MGT books are worth more than their asking price. To me, they are. To someone else, they either are or aren't depending on more factors than can be enumerated in a reasonable post, or thread.
Why I play Traveller without the OTU:
I played it for 30 years without the OTU. The OTU is a setting, once commonly called the "Imperium Campaign" as I recall. Traveller was originally sold without it. The tech assumptions inserted in the original rules are not the universe, they're a constructive response to the constraints encountered in writing and publishing a rule set.
If you look at the literary inspirations for the Traveller rules you'll find those tech assumptions, or something very close to them, in many books from many authors. None of them was writing about the OTU. The tech assumptions are not based on science so much as dramatic logic. You don't have instantaneous communications so that the characters have freedom of action. You have limits on travel speed to enlarge the feeling of space in the story. Large areas with poor communications implies that local governers have lots of control, which implies an imperial or feudal system of government when our own history is consulted for analogues (or when our own history is mined for stories to tell in space, take your pick.)
As it happens, these dramatic choices work well for an RPG. And that's all Traveller was written to be.
Then RPGs grew, and Traveller and many other games learned the same lesson that came with the VCR and the disposable razor: the money to be made is not in the sale of the original equipment, but in the media it consumes. Hence the OTU.
The OTU is almost certainly responsible for Traveller being something other than one of those games that kicked out a rulebook then disappeared before 1982. But it's not Traveller.
Why do I use the Traveller system? Simple. Because it's the only skills-based system that has effectively limited skill bloat, constant increases in the lists of skills, and non-skills-based rules appendages to stay a quick, easy to run, rules-light system without constraints like character classes.
BRP hasn't managed this, Gary Gygax's systems haven't managed this (from Cyborg Commando through Lejendary Adventure), GURPS
started out too heavy. CoC (non d20) has managed to some degree, and I can always pull out my old RQII, I suppose. There are others that are close, but for a short list of broad skills that aren't built to, like Topsy, just grow, Traveller takes the cake. Though I wouldn't say this is true of all versions of Traveller--I can say it for the two versions I play. MGT still has the opportunity of going skills list happy, but I don't have to participate.
Traveller also suits the games I want to run right now. I like SF, I like running SF games that are like the stories I like to read. Traveller gives me what I need to bring those ideas to the table easily. The OTU material I've acquired is good stuff to mine for ideas, scenarios, etc. The mechanics of Traveller are far more flexible than the OTU would imply at its surface, I feel. SOC doesn't have to mean feudal nobility. It's perfectly possible to design another ship building system and still have it be Traveller.
Here's a challenge for those who care to give it a try. In the OD&D circles, something newer (post-1976) players will sometimes do is try playing the game with nothing more than the first three books and Chainmail, or possible add Greyhawk and the early articles from The Strategic Review and first few issues of the Dragon.
How about some folks give a try to playing Traveller with just the first 3 books? I've run about a year's campaign giving the OTU a spin. It didn't work for us as-is, but the experience was certainly invaluable for me. I now know enough about the OTU to make far more effective use of its materials in any game than I did before. I can read OTU stuff and make sense of it without having to look up every third race or place name.
Give Traveller a spin without the OTU. Leave behind every race, place, and assumption it makes. Read the first 3 books, 1977 edition if possible, with "new eyes" and build a game from some of your favorite SF. See what you can make fit, and see how well you can write rules to mesh with what doesn't.
I've used Traveller to run everything from "Sticks and Stones" style games to H.G. Wells and Verne-style adventures (before it was "steampunk") to cyberpunk to a number of different literary SF venues and mixes of them. I'm no super-gamer, I've just been at it for a while. I think that those who think Traveller is just a setting might gain some new appreciation for the rules and how well they work if they give this a try.
With several bushel boxes
full of rules in my closet, over twice as many in the garage, and an income that allows me regular visits to the FLGS, I play Traveller because I want to, not for lack of choices.