There are games out with multiple versions available, thanks to the "long tail" provided by internet based sales, like Dungeons & Dragons and Traveller to name two. So how do you choose which version to buy? What are the criteria that you evaluate before you purchase? What information goes into the decision process?

Very easy: The version that I can get.
Chances are that if I truly like the game's rules or setting that I will try to hunt down other versions to get the full picture and decide for myself which one suits me best.

Some games I discovered in their order of publication ...

• RM --> MERP --> RM2 --> LotR Adventure Game --> MERP2 --> HARP
  
• Midgard I --> II --> III --> Abenteuer in Magira --> IV
  
• Talislanta 2 --> 3 --> 4
  
• Nephilim v1 --> v2 --> Chaosium Nephilim --> v3
  

... others I discovered in the midst of their life and meandered back and forth in their publication history ...

• Mentzer Basic --> AD&D1 --> AD&D2 --> RC --> Holmes Basic --> D&D3 -->  Moldvay via Labyrinth Lord --> D&D4 --> White Box via Swords & Wizardry
  
• dK System --> dK2 --> Lanfeust de Troy
  
• FanPro Traveller (The Traveller Book?) --> MegaTraveller --> TNE --> T4 --> Classic Traveller LBB
  

... with the bolded versions being the ones I ended up liking most. No system to it. (But there is a pattern that I can see now - it's the most compact, or lite, versions that I fancy most.)

Quote from: Dirk Remmecke;352690Very easy: The version that I can get.

Good answer, but with ready availability of multiple versions of a game, the next most practical answer is: The version that I can get other people to play.

I have my classic favorites, and I can often get new-comers to play them, but there's an undeniable cachet to recent editions.  I'm finding, over time, that I need to adapt.

!i!

I read product descriptions, reviews, and internet blathering. I go find one in the store if I can and look at it. I pick the version that looks most concise and least burdened by canon material.

Quote from: Halfjack;352718I read product descriptions, reviews, and internet blathering. I go find one in the store if I can and look at it. I pick the version that looks most concise and least burdened by canon material.

This pretty much sums it up.

If I hear people loved 2nd edition of a game but HATED 3rd edition, I lean toward second edition...unless I'm reading reviews of 3rd edition and the changes sound like things I LIKE.

On the surface, that was how I was with D&D 3rd...all the changes SOUNDED good.  In practice, it wound up being way more work for me than AD&D2e, which I ran successfully for years over multiple campaigns, ever did.

It depends.  I try to go for the BEST edition, or the one that does what I want it to.

Being cheap, or being the one I started with or got the most stuff for dirt cheap is also a big selling point.

Its usually an older edition over a newer one though.  

Its not the D&D/Magic/40K trinity so its all fucking niche as shite anyhow so why worry about other people getting it when it really doesn't matter all that much anyhow since I usually have to provide the books and such to begin with?

One can always get all the editions. Or the one that was clearly the best one.

RPGPundit

I play(test) and then decide. Once the decisions is made, I go to Amazon / Ebay to hunt down the product line. (I'm a voracious RPG buyer, and a huge bibliophile as regards RPG products, as I simply love having the stuff on the table for the game I'm playing.)

So far I've been only interested in RPGs which had playtest versions freely available on the 'net, either produced by the publisher or a fan. Just consider FFG's RPGs - you can download a basic version of the rules and 2 demo adventures each for Rogue Trader and Dark Heresy. That's enough to effectively decide between which product line to invest in or not invest in one at all.
Or take WotC. All of their D&D 3E rules are available in the SRD (still available on the WotC website, though you want one of the fan-created hyperlinked versions), and WotC even created a "test drive" file for 4E, the complete Shadowfell module and starter ruleset.

We really do live in an age where test driving RPGs has become the norm. Older editions are usually fan-supported, and test drives of these (if not downloads of the entire ruleset) are just as  obtainable on the internet. Which is why WotC' removal of older edition PDFs was so inane. You literally can't remove stuff from the internet for good. You just can't.

If I am buying a game to play, then I look for the edition with the most active players.

First benefit: the largest group gravitates towards the most playable game.

The two other benefits :

1. minimum effort finding and organizing a game.
2. a larger group means more people you can choose from, so you get people that you like. You are never forced to deal with people you don't like just because they're the only ones willing to play.

Honestly, I find most games don't change substantially from one edition to another to really worry about doing anything but getting the latest one.

Exceptions are Traveller (which ceases to exist after MT AFAIC), D&D (there can be only 3rd), BESM (All of the editions are terrible), GURPS (4e is not GURPS, it's HERO as pointlessly reimplemented by Sean Punch), and Gamma World (they're all sort of broken, but 4th is the easiest to get into).

I tend to go for the earliest widely-available edition, which is usually the first but may be the second if the first was released by an ultra-small press or was almost-immediately superceded (in which case I look at the "2nd" as the actual first, and the "1st" as the "beta"). Early editions usually feel more "authentic" and closer to the designer's "heart" to me, with each subsequent edition becoming increasingly faceless and corporatized as the production becomes slicker and more editors tinker with the text and mechanics. That said, for games that remain largely the same from edition to edition except for art and corrected errata (e.g. Chaosium games) I may just pick up the latest/current edition -- I've never felt the need to own a copy of Call of Cthulhu earlier than the 3rd edition, for instance, and if I were to play it again I'd almost certainly use my 5th edition hardback (the latest edition I own).

I tend to buy the first edition.  I want to see the original concepts and the original, often raw creativity.   Ebay is great for this.

Then I tend to bang on the system until I'm happy with it.   Rarely do I need to pick up other editions, unless they have a radical redesign that catches my interest.

Mostly I just pick what seems to be reasonable to run (as a GM), or what seems the most fun/cool to play.  Sometimes these things are at odds, and I have to weigh things out.  I'll usually go with the better system if I can patch on bits from other games I like.

Quote from: J Arcane;353156D&D (there can be only 3rd)

3.0 or 3.5?  

I have a love-hate relationship with 3.x, though.  It's the first game system I ever learned and I have a lot of good memories, but the powergaming culture surrounding it really kills it for me sometimes.