Slav Defense or Queen's Gambit Declined?

Which one is harder for white to beat? Which one is more solid?

Both are excellent openings. Solid is in the eye of the beholder. Both openings can be learned at a rudimentary level in a weekend and both will serve you for the rest of your life.

Against top players, the QGD tends to be a bit more passive than the Slav. So if you want to strive to win as Black, the Slav is probably a slightly better choice.

For novices (and for people asking the question), The QGD Tarrasch is probably the best way to get a good playable position. That line goes:

1.d4 d5 2.c4 e6 3.Nc3 c5. The center usually opens up and Black gets to develop his minor pieces comfortably. The only drawback, and it's a minor one, is that Black usually has an isolated queen pawn (IQP). But even that is good because as Nimzovich stated, learning how to play with (and against) an IQP is a major step toward understanding positional chess.

Agree with SmyslovFan for the QGD Tarrasch. This is an opening in which i feel comfortable.

IMO the slav is (far ?) more complex to hold on for a beginner/amateur, i think it requires a serious preparation. 

However, both QGD and Slav can be solid defense.

I Prefer Slav 

I can play both and have played both (along with the Tarrasch).  Some differences to keep in mind:

1) The Slav eliminates the Catalan as a viable candidate.  Yes, White can play an early g3, but it's just not good, and Black gets easy equality, possibly even a slight edge.  The downside is that you either have to relinquish the center with 4...dxc4 or else play 4...e6, which keeps the bishop behind the pawn chain anyway.  The former is the Slav, the latter is the Semi-Slav.  1.d4 d5 2.c4 c6 3.Nf3 Nf6 4.Nc3 Bf5 is bad on account of 5.cxd5 cxd5 6.Qb3!  Another downside is you have to deal with the exchange variation, which can be very drawish.

2) The Queen's Gambit Declined has the advantage that the "Exchange Variation" is non-symmetrical.  The ideas are pretty easy to grasp (easier than the Slav).  The downside is that you often have to defend for a long time before you can attack.  You also have to know what to do against the Catalan.

3) The Tarrasch Defense has the advantage that if White plays the Catalan, no problem, you simply play the Tarrasch.  The main line involves White fianchettoing the Bishop anyway.  It's also a little more active than the QGD.  The downside is pawn structure.  You end up with an isolated d-pawn or doubled isolated c-pawns, so you have to know your theory or you'll get blown off the board.  Active piece play is of paramount importance, and you can't be afraid to take doubled c-pawns, doubled f-pawns, or an isolated d-pawn.

I play all 3, but do have a slight preference for the last of the 3.

If playing for a win, go with Slav. if draw is enough, QGD.

saying an opening is drawish is hugely irrelevant for the vast majority of the people who play chess. it is very rare that either me or my opponents can play accurately enough to make a drawish position turn into a draw. i really wouldn't worry about something being "drawish" if i were you.

I think I said it poorly. If you prefer a fighting game where both players are looking for combinations, the Slav is the game for you. If you like a waiting game where one can wait till the endgame until someone plays a bad move and you take advantage, QGD. This is just my opinion.

Uhm, that might be true for you, but drawish lines often turn into draws when you start reaching Expert and Master level.  Doesn't take a GM to draw the Exchange Slav.

I've been an Expert for 10 years, working on reaching master.  Don't go by my 5-minute rating here.  I experiment with new openings here and also don't find 5-minute nor internet chess to be an accurate assessment of a player anyway.  Chess on Chess.com or ICC is equal to Garbage Chess.  Over the Board and Correspondence are what count.

Pelik, my argument was that the downside of the Slav Defense is having to deal witht he exchange.  It tends to be drawish, and you proved the statement yourself, it's Black that has room for error because symmetrical positions give White the slight edge due to going first.

Therefore, if you are playing Black, and face an exchange Slav, first you have to play accurate moves immediately after the opening, and then find some way to take advantage of what would need to probably be multiple errors by White just to win it.

So yes, I consider facing the Exchange Slav as Black a downside to the opening, ESPECIALLY if you are facing a lower rated player!

That's why I prefer the Tarrasch, and only play the Slav sometimes against higher competition.

I play the Slav against lower-rated players because there's no way they understand the Exchange variation well enough to give me trouble. There are drawbacks to other move-orders as well.

An early g3 against the Slav is definitely not going to give Black the edge(ridiculous comment there), and the lines involving Qc2 and g3 are very dangerous.

Interesting.  When I was 1400, I used to play the Exchange Slav as White, and got many draws against 1700 to 2000 players.  I'd usually win against the other 1400s because I was underrated.

Since then, now being about 2050, I played the main lines, specifically the Central Variation (6.Ne5) until players quit playing the Bishop Sacrifice and started playing 6...Nd7.  Since then, I've been playing 3.Nc3 and 4.e3 with good results.  I did take a bad loss not long ago, but most of mine end up wins.  I either end up in a Quiet Grunfeld line if they play 4...g6 or an Anti-Meran Semi-Slav (i.e. 6.Qc2 instead of 6.Bd3, and if they play 6...Bd6, I go for the Shirov Attack, 7.g4) against legit players, and when I play down, I often get 4...Bf5 with advantage to White after trading on d5 and playing 6.Qb3.

Sure, Black can draw easily in the Slav Exchange if White goes for the dry 1.d4 d5 2.c4 c6 3.cxd5 cxd5 4.Nf3 Nf6 5.Nc3 Nc6 6.Bf4 Bf5 7.e3 e6 8.Bd3 Bxd3 9.Qxd3 Bd6?! (throwing away hopes for imbalancing the position; I think 9...Be7 is best keeping the good Bishop now that White has traded his good one) 10.Bxd6 Qxd6 (this line has been played many times but most likely in situations where the players had agreed to a draw before the game). More challenging are 8.Bb5 and 8.Qb3 but Black has resources sufficient to imbalance the game, often giving up a pawn for open lines on the Queenside. Also 4.Bf4 Qb6!? is interesting (for White). It's a fascinating line where I have actually never drawn a tournament game as either color (scoring 100% against non-GMs and 0% vs GMs) with at least thirty tournament games against players rated between 1800 and 2350.

yes exactly. most people, particularly the type of person who is asking if the slav or qgd is more solid, are not expert or master level!

Agree. I can definitely not manage a drawish opening to a draw most times, but knowing some openings gives me a fair chance in the mid and end game. Not knowing the openings always puts me slightly behind after the opening.

I always do slav. Especially in bullet where you want to be as solid as posiible. I look at it like this. The gambit is supposed to be tricky so why play into it? Just develope quickly, castle with the slav, and have a soild middle and endgame center.

the slay is better

On the internet dependent on the venue, my elo is between 1400 and 1800. I play the Orthodox Vaiation of The QGD and have come to the same conclusion. VERY rarely will play diminish into a drawish position at my level.... My view of the Orthodox (and hence my view of most openings considered drawish) is they have a lot of defense inheritly built in to the resulting positions... and I'm not talking playing passive either.. Oftentimes (and this probably can be said about many defense, but I think it really applies with the Orthodox) when White over reaches the positions boomerang in Black's favor.

I feel like queens gambit declined is harder for me when I'm playing as white, but it can vary for a lot of people

The Semi Slav and Slav are much better options than the passive Queens Gambit Declined