The Mongoose Traveller system (or MGT for short) lies closest to original Traveller in its design, but it has been streamlined for a more modern design.
Huh?
The game that lies closest to the original design
is the original design, and it's still in print.
Its been updated to reflect a more modern sense of how the future will look (i.e. computers no longer take up tons of space).
Will this myth never die?
A "one displacement ton computer," which is the Model/1 you find on the ubiquitous
Beowulf-class free trader, consists of a desk with a workstation and a chair. That's a "ton" of computer in
Traveller.
And you can buy a hand computer with the same performance, but less withable to stand a hit from a 250 megawatt laser or a high-explosive missle, which is something a starship computer can manage.
The reprints of "classic" Traveller from Far Future Enterprises / Marc Miller are the old Traveller books, just like they were in the old days. The game still holds up exceedingly well after all these years and the other editions that I've seen (Mega, T4, D20 and Gurps... I haven't looked over the others) just don't hold a candle to the original. The original is a rules light, adaptable sci fi game that you can use for anything.
Yes.
I own roughly a displacement ton of original
Traveller books (to me calling it "classic" is superfluous), supplements and so forth, and I also have the Mongoose edition core rules. The only reason I can see to buy the Mongoose version is if you insist on having a system which is presently supported by newly published material.
My recommendation is to get the two "classic" CD-ROMs: one disc contains the complete GDW canon (every rulebook, adventure, supplement, even every board game produced for
Traveller) and the other disc contains the complete run of the
Journal of the Travellers Aid Society, the
Traveller magazine, which is also full of adventures, equipment, rules variants, and so forth. Each disc is U.S.$35.00, so for $70.00 (less than the Mongoose core rules plus one supplement) you can have roughly ten years of published material. I don't think there's a better deal in gaming, myself.