Falkbeer counter-gambit!
Best opening against white's King's Gambit?

Practically, I'm with WittyBlunder. Most white KG players don't learn the falkbeer like they do the KG.
It's not that it's the strongest, but that it throws them off their game easily enough in most cases below 1500 in live.

if you're more interested about Falkbeer counter-gambit search IM "chessexplained"'s videos on youtube about King's gambit.

After 2.f4 d5 3.ed e4 - (as said in previous comments, this is the most popular but not the most unpleasant way for White) - 4.d3 and here (I refer to the moves which my opponents applied, beginning from weaker to stronger ways of Black):
4. ... Bf5 5.Nc3 Nf6 6.de Nxe4 7.Qe2;
4. ... ed - here 5.Qxd3 and 5.Bxd3 are equal and both are good;
4. ... Qxd5 5.Nc3 Bb4 6.Bd2 Bxc3 7.Bxc3 Nf6 8.Bxf6 (immediate 8.de is also good, but capture on f6 is more to my taste) gf 9.de Qxe4+ 10.Qe2 Bf5 11.0-0-0; or 7.Bxc3 Ne7(!) 8.de Qxe4+ 9.Qe2; or 7.Bxc3 f6 8.Qe2;
4. ... Nf6 (the most popular and the most promising) 5.de Nxe4 6.Nf3 (this is the most popular and really the strongest for White; 6.Be3 is rather popular (the idea is to prevent Bf8-c5) and also belongs to the mainlines, but Black gets not a bad position at all after 6. ... Qh4+ 7.g3 Nxg3 8.Nf3 Qh5. Still it seems that even 6.Qf3!? Qxd5 7.Nd2 might be better for White than 6.Be3. As for the fresh ideas I've been working upon - there are two interesting ways here - 6.Qd4!? and 6.Qd3!? - I tried both of them only in blitz games for now - with not bad impressions, and after some deeper elaboration I probably will try some of them or maybe both of them in correspondence games, too), so - 6.Nf3 Bc5 (the most popular but not the strongest, 6. ... c6 is played not so often, but looks more promising - I play 7.Nbd2 here, and there is one more good way - 7.Bc4); instead of 6. ... Bc5 and 6. ... c6, Black sometimes plays calm 6. ... Be7 - the way for White which I like here - 7.Qd4 Nf6 8.Nc3 0-0 9.Be3 Nbd7 10.0-0-0; and there is one more way for Black - 6. ... Bf5 - Black does not struggle for the diagonal a7-g1 - White has a comfortable position after 7.Be3). So, the key position (or one of the key positions) of the Falkbeer Countergambit arises after 6.Nf3 Bc5 7.Qe2
The main ways for Black:
A) 7. ... Bf5 (the most popular) 8.Nc3 (typical mistake (or whatever it may be called) of White here is 8.g4!? - it's risky, and although it doesn't lose, there may be some nasty consequences for White after 8. ... 0-0! 9.gf Re8 10.Qg2 Nf2+ 11.Be2 Nxh1 - the position is equal and sharp. The only thing White may hope for is that Black does not play 8. ... 0-0) Qe7 9.Be3;
B) 7. ... Qe7 (not so popular, but good) - here both 8.Nc3 and 8.Be3 are good for White, I prefer the bishop move;
To the more or less often playable ways of Black we can aslo refer:
C) 7. ... f5 - this move occurred in one of recent VC games where I participated. Although our opponents were lucky to end that game in a draw, I made conclusions (and analysis of the opening phase, too) after that game - 8.Nfd2 (8.Be3 is playable, too, but the knight move looks more promising) 0-0 (8. ... Bf2+ leads to unpleasant consequenses for Black, likewise 8. ... Qxd5) 9.Nxe4 fe 10.Nc3;
And some more ways of Black after 7.Qe2, which are weaker, though:
D) 7. ... 0-0 8.Qxe4 Re8 9.Ne5 f6 10.Nc3, or 9. ... Nd7 10.Bd3 (10.Bb5 and 10.Nc3 are good, too), or 9. ... Qh4+ 10.g3;
E) 7. ... Bf2+ 8.Kd1 f5 9.Nfd2;
F) 7. ... Qxd5 8.Nfd2.
It's really better for Black to play (1.e4 e5 2.f4) ef or (1.e4 e5 2.f4 d5 3.ed) ef

That is interesting. Couldn't white simply play Nc3 after Bf5 though to further the attack on the pinned Knight? Black would be forced to either castle or play Qe7. Just saying :).

SithLordsOfLegend wrote:
That is interesting. Couldn't white simply play Nc3 after Bf5 though to further the attack on the pinned Knight? Black would be forced to either castle or play Qe7. Just saying :).
Line A) in green? Just sayin'.

Practically, I'm with WittyBlunder. Most white KG players don't learn the falkbeer like they do the KG.
It's not that it's the strongest, but that it throws them off their game easily enough in most cases below 1500 in live.
Falkbeer Countergambit does make a part of King's Gambit, and it would be at least naive of KG players to hope that opponents would play 2. ... e5xf4 only. As for statistics of my games (both blitz, OTB and correspondence), me playing as White, I can say more or less definitely that upon 1.e4 e5 2.f4 the opponents play
2. ... ef - about 50%
2. ... d5 - about 15%
2. ... Bc5 - about 15%
2. ... d6 - about 15%
other (2. ... Nc6, 2. ... Nf6, 2. ... Qh4+, 2. ... Qf6, 2. ... f5, 2. ... f6 etc.) - about 5%
Of course I did not keep precise statistics, but anyway
Is there software to determine what opening you are in, as moves progress? I have never been successful studying openings but I'd like to because it must be nice to play right in the beginning(an edge).
My journal if you're interested --> Chess is keeping me sane during some transitions,
http://btlsp2000.tripod.com/a-inkwell/inkwell.html