I like all three versions for different reasons.
V1, the original grandaddy of them all. The timeline works for the most part, just have to imagine the cold war never ended. Most of the supplements out there are for V1. I don't like how it grouped "shots" into 3 rounds of ammo.
V2/V2.2, streamlined character creation and rules, although I liked the damage charts for V1 vehicles, need to know what happens if your T-55 upper left front glacis is penetrated by a HEAT round? well then they have damage charts for that. V2/2.2 has additional nationalities and careers in the rulebook. You wanna be a Belgian actor/French Foreign Legion paratrooper/idle rich millionaire/politician, well you can, but everything is broken into 4 year terms. Timeline was updated to the RL 90's but it needs some jiggering. More modern vehicles in the books. V2.2 characters are compatible with Traveller rpg.
Despite all this, I personally like 2.2, but that's just me. Most people prefer V1 though.
Do you absolutely positively need a real physical copy of the rule books? Keep in mind T2k has been out of print for well over a decade so getting copies of supplements will be hard.
If you don't absolutely positively need a real physical copy of the rule books printed in the 80's or 90's, drivethrurpg has been mention, but what about buying a copy on CD?
You can get copies of everything ever printed by GDW for Twilight 2000, including Challenge magazine articles on CD through Farfuture. One CD for all V1 and one CD for all V2/V2.2. I would imagine you could print them out for your tech challenged friends as well.
http://www.farfuture.net/FFE-CDROMs.html