I suggest using Stockfish to explore the opening. If you cannot see why Stockfish does what it thinks best then try your move and find out why it is (nearly always) inferior.
Here is my exploration of the opening:
Variant 1
1 Nf3 f6 2 e3 d6 3 Nd4 Nh6 4 Nb5 Ng4 5 f4 Nf2 6 Qh5+ g6 7 Nxc7 gxh5 Black is a piece and 2 pawns down +6.
S: 5... Be6 6 Nxc7 g6 7 Bb5+ Kd8 8 Nc3 Bd5 +8.2.
S: 3... Bg4 4 f3 Bf5 5 Ne6 Bxe6 looks fairly even +3.2. This is the refutation.
S: 2... d5
Variant 2
1 Nf3 f6 2 e3 d6 3 Nd4 c6 4 Nc3 Bg4 5 f3 Bf5 6 Ne6 Bxe6 7 Bb5 a6 8 Nd5 e5 9 Nc7+ Qxc7
S refutes this with 3... Bg4 as above.
Variant 3 S thinks this is the best opening
1 Nf3 f6 2 e3 e6 3 Nd4 c6 4 Nc3 a6 5 Nf5 exf5 6 Nd5 cxd5 White mates in three: 7 Qh5+ g6 8 Qd5 and mate. The idea: once the c and e pawns are gone, the queen mates.
S: 6... Bb4 7 c3 Nh6 8 Nb6 Qxb6 9 cxb4 Ng4 10 f3 d6 11 Qb3 Be3 12 Qb6 O-O 13 Bc4 Kh1 14 Qc7 Bd7 15 fxg4 c5 16 Bg8 h6 +8.8 Black is down queen for piece and pawn.
S: 4... Nh6 5 Ncb5 Ng4 6 f4 cxb5 7 Bb5 Nc6 8 Nf5 Bb4 9 c3 d6 10 d3 a6 11 Ne7 h5 12 Kf1 Bd7 13 Bxc6 a5 0.0 but highly tactical. If 12 Nxc8 then 12... f5 13 Bxc6 Rc8 14 h4 Nf7 15 Qf3 d5 +2.9 so this is better for white than 12 Kf1
S: 3... f5 4 Qh5+ g6 5 Qh4 Qxh4 6 Nb5 a6 7 Nxc7 Bd6 +6.2 Black is piece and pawn down.
S changed this to:
S: 3... c6 4 Nb5 cxb5 5 Qh5+ g6 6 Qb5 Nc6 7 Qb6 axb6 8 Bb5 Kf7 9 Bxd7 Nh6 10 g4 Rxa2 +5.0 White has two pawns for a piece
S: 2... d5 3 Ng5 fxg5 4 Qh5+ g6 5 Qe5 Be6 6 Qxc7 b5 7 b3 Nf6 +3.7 Black is down 2 pawns. 8 Ba3 b4 9 Bb5+ Kd8 10 f3 Ne4 11 fxe4 Bg7 12 Rf1 Bxa1 13 Bb2 d4 +5.0 White is down the exchange for a pawn
Variant 3a
1 Nf3 f6 2 e3 e6 3 Nd4 f5 4 Qh5+ g6 5 Nb5 Qh4 6 Qxh4 a6 7 Nxc7 Nf6 Black is piece and pawn down +5.8
S: 6... Nf6 7 f3 a6 which is the same, just different move order
S: 3... c6 4 Nb5 cxb5 5 Qh5+ g6 6 Qb5 Nc6 7 Qb6 axb6 8 Bb5 Kf6 9 Bxd7 Rxa2 10 b4 Bd6 11 f4 Na6 +5.6 Black has an extra knight, white 2 pawns
S: 2... d5 as above
Variant 4
1 Nf3 f6 2 e3 e6 3 Nd4 c6 4 Nc3 Nh6 5 h3 a6 6 Nf5 exf5 7 Nd5 Bb4 8 c3 f5 9 Nb6 d5 10 Nxc8 Bd3 +9.8 Black is down queen and pawn
S: 8... d6 9 Nc7+ Kf8 10 d4 g6 11 g4 d5 12 f4 Kg8 13 e4 Nf5 14 gxf5 f5 +6.0 Material is even but white can win a rook
S: 6... Nxf5 7 Ne4 g6 8 Be2 a5 +0.9 Material is even and the position is quiet
S: 3... f5 4 Qh5+ g6 5 Nb5 Qh4 6 Qxh4 a6 7 Nxc7 Nf6 8 f3 Bd6 +1.2 but black is down piece and pawn
Variant 4a
1 Nf3 f6 2 e3 e6 3 Nd4 c6 4 Nc3 Nh6 5 Ndb5 cxb5 6 Nb5 Bb4 7 c3 Ng4 8 f4 Na6 9 Nxa7 Ba5? 10 Bb5 Kf8 11 Bxd7 Ke7 Black is down queen, rook and 3 pawns for bishop, worse still white has mate in six
S: 9... b5 10 a4 Ba3 11 Bxa3 O-O 12 axb5 g6 +7.2 Black is down rook and pawn
S: 8... h5 9 Nxa7 O-O 10 Bb5 Nf2 11 O-O Qb6 12 Bc6 Qd4 13 cxd4 bxc6 14 Qa4 Bb7 15 Qc6 g5 16 b3 Ba6 17 Qxa6 Kh7 +5.5 Black is down the exchange and two pawns
S: 7... O-O 8 Nxa7 Ng4 9 f4 h5 10 Bb5 Nf2 11 Kf1 Qb6 12 Bc6 Qd4 13 exd4 bxc6 14 cxb4 Bb7 15 Qf3 g5 16 Qc6 Ba6+ 17 Qxa6 Nd3 +5.2 Black is down rook and two pawns
S: 6... Ba3 7 c3 Qa5 8 bxa3 Ng4 9 f3 Nf2 10 Qb3 O-O 11 Nd6 Qxa2 12 Nxb7 Nxh1 +2.0 White has two bishops to black's rook
S: 5... Ng4 6 f4 cxb5 7 Nb5 Ba3 8 Bxa3 Qa5 9 c3 Qa4 10 Qc2 Nf2 11 Nd6+ Kf8 12 Ba3 Nd3+ 13 Ke2 Nc1+ 14 Kf2 Nd3+ 15 Qxd3 Qe4 16 Nxe4+ d6 +2.7 Material is even NB 15... b6 allows mate in two
S: 3... f5 4 Qh5+ g6 5 Nb5 Qh4 6 Qxh4 a6 7 Nxc7 Nf6 8 f3 Bd6 +1.6 Black is down knight and pawn
Variant 5
1 Nf3 f6 2 e3 e6 3 Nd4 Nh6 4 Nb5 Ng4 5 f4 Bb4 6 c3 c6 7 Nc7+ Kf8 8 cxb4 Na6 9 Bxa6 h5 10 h4 Nf2 11 Qa4 Nd3+ 12 Kf1 Nxb2 13 Qd4 d6 14 Qd3 g6 15 g4 b6 -7.8 Black is rook and pawn up but it is unclear.
S: 9 b4 g6 -0.9
S: 8 h3 Nh2 9 Rxh2 g6 10 d4 h6 11 e4 d5 +4.0
S: 3... f5 4 Qh5+ g6 5 Nb5 Qh4 6 Qxh4 Nf6 7 f3 a6 8 Nxc7 Ne4 9 fxe4 f5 +2.2 but black is two pieces down. 8... Ne4 seems pointless.
Variant 6
1 Nf3 f6 2 e3 e6 3 Nd4 Nh6 4 Nb5 Bb4 5 c3 Ng4 6 f3 Nf2 7 Qa4 c6 8 Nc7+ Kf8 9 Ne8 g6 10 d4 Ba3 11 b3 Bxc1 12 Nd6 Qa5 13 Nxb7 Kg7 14 h4 h5 15 g4 Nxh1 16 Qxa5 hxg4 Black is down bishop and pawn +6.5
S: 16... g5 but still +5.5
S: 15... Rb8 but still +5.0
S: 14... Nxh1 +6.0 ie worse
S: 13... Qb5 +5.5
S: 12... b5 13 Nxc8 bxa4 14 g4 d5 15 Ba6 e5 16 f4 Rd8 Black is a pawn down but can win the exchange +0.3
S: 11... Na6 12 Qb4+ Bxb4 13 Nd6 Nb4 14 Be2 Nxa2 15 Nxc8 Nxh1 -4.9 Black is up two exchanges and 2 pawns. This is by far the best line for black.
S: 10... Na6 11 b3 d6 12 e4 h6 13 e5 Ba3 14 Bc4 Nb4 15 O-O Bxc1 16 exd5 c5 -3.3 unstable situation, black a piece up
S: 9... g5 10 Nd6 Bxd6 11 Qb4+ c5 12 Qxb7 d5 13 Ba6 h5 14 d3 d4 15 Na3 h4 +2.0
S: 4... Ng4 5 f4 Qe7 6 Nd6+ Qxd6 7 h3 Nf2 8 Qh5+ g6 9 Qb5 b6 10 Qxb7 Ne4 11 d4 Nd2 12 Ba6 Nxb1 +3,6 Black is down a pawn
S: 3... f5 4 Qh5+ g6 5 Nb5 Qh4 6 Qxh4 a6 7 Nxc7 Nf6 8 f3 Bd6 9 e4 fxe4 10 d4 h6 11 Nc3 O-O 12 Ne4 Bf4 13 Be2 Nd5 14 Nf6+ Kh8 15 Bxf4 Nf4 16 Bd1 Nxg2 +2.5 Black has rook for two pieces
I've started work on a documented list of possible ways to defend against 1. Nf3 2. e3, as it seems to be the main reason I lose as well as why many people dislike atomic. However, while documenting, I came across many different variations varying from extremely popular to weirdly niche. I wanted to cover at least all the mainline or gambits to have people covered, but it seems like that will take several ages. So, I wanted to know at least what were your top picks for the opening. In this position (white to play), what would you do?