What would you recommend for Black against the Queen's gambit?

I usually play ...Nf6 against 1.d4, but after reading repeated warnings that the Indian defense is too complicated for a beginner I've opted to play the Queen's pawn game instead. What line would you recommend against the Queen's gambit?

Used to play the Benoni, switched to the Tartakower var. Much safer, if maybe a bit boring.

golabomb, I meant to write ...Nf6 in my (now edited) opening post. I don't want to play the King's Indian because of its supposed complexity. I would prefer a simpler and less theory-driven opening to play.

If you are a beginner then queen's gambit declined is the way to go. Lasker leads to clearer position than Tartakower and is less confusing LOL. Here is Kasparov on "how to play the Tartakower."

I've always thought that for beginners, the Chigorin (1.d4 d5 2.c4 Nc6) made far more sense than the QGD.

I think the latter mostly gets recommended because it's the opening that GM's use that also flows most naturally from an initial central, symmetrical pawn move.

But the QGD tends to play out as a subtle, positional game with lots of in-between moves, timing issues, radical redeployments of knights and such.

The Chigorin is no doubt inferior at the GM level.  The intially blocked c-pawn, if given freedom to move, has proven over the years that it will give you slightly better chances agaisnt GM level opposition.

This shouldn't be an issue for a beginner.

In the Chigorin, the knight gets deployed to its most obvious and sensible square, the games tend to be very open with a lot of piece play, and the timing issues and subtle shifts in plan aren't nearly as prevalent.  Play for ...e5, which is where the most general precepts of opening theory tell beginners pawns want to be anyway -- on those central squares.

As a runner up, the QGA is a good choice.

The best defense against d4 is probably a combination of Nimzoindian,Semi-Slav and a little bit of KID.It's all about the transpositions.It would be better to expose yourself to alot of openings in the long run I think.

But if you want to cut it down I'd say the QGD is the most principled

And the KID is the most fun

My thoughts on the matter are that if you need to ask, you should probably be playing the QGD(maybe the Tarrasch, Lasker, or Tartakower variation.)

         I like the Budapest Defence.

You don't know what that is?  Hmmmm. . . .

Only because I dislike playing against the D4 opening.

The Lasker defense saw a spurt of popularity a few years ago due to the final game of the Anand - Topalov match:

The Albin Counter-Gambit!

this is surely true in theory.

but how do I know if I understand d4/d5?

Tarrasch is good for your overall chess improvement, you learn how to play with the isolated pawn which is a very important skill. Isolated pawn formations are rather frequent and can result from various openings.

You might try Blumenfeld gambit, too. Black gets powerful pawn centre if white accepts the gambit. It is a bit similar to Benko but has much less theory because it is not played frequently.

If you only wanted something good I would recommend Nimzo-Indian. Since you need something with little theory it is definitely not a good choice (Nimzo is not much less developed than KID)

Don't shy away from theory.Play what you enjoy playing first and study them.When you get bored try something else.Sure the KID has alot of theory,the Nimzoindian has a lot of theory but you can wing this openings using principles alone.You can fix the difficult positions later on as you play them.Playing a variety of d4 defenses will help you in the long run especially if  youre a d4 player yourself as white.

I am about your level and have had decent success using the Old Benoni and the Budapest.

This could be further from the truth, but not much.