[FEN ""] 1. e4 e5 2. Nf3 Nc6 3. Bc4 Nf6 4. Ng5 d5 5. exd5 Nxd5 6. Nxf7 Kxf7 7. Qf3+ Ke6 8. Nc3 Ncb4
White can play 9. Qe4 (Old variation protecting c2 square from ... Nxc2+ forking King and Rook and also with attack of d4 etc.
White can also play 9. a3 allowing 9... Nxc2+ 10. Kd1 Nxa1 allowing Black to attack the Rook. Further White will play strong attacking moves like 11. Nxd5 etc. and continue the strong attack.
Is 5... Nxd5 correct or he should go to main line of Two Knights Defense with 5... Na5?
After 5... Nxd5, can White continue with 6. Nxf7 for strong attack?
After 7. Qf3+, can Black continue with 7... Ke6 challenging White in further game? Hence can we play 7... Ke6 in tournaments and continue our attack and study of opening variations?
Between 9. Qe4 and 9. a3, which variation is better for White?