1. e4 e5 2. Nf3 Nc6

After these moves, what third move for white leads to the most aggressive game? is it 3. Bb5, 3. Bc4, 3. d4, or is it something else? I'm not talking about the most aggressive third move, I'm talking about the most aggressive game overall. 

I'm currently playing Bc5 because I really believe it leads to many aggressive lines, but there are still some lines that are really really boring. 

3 bc4, you have ng5 against the two knights and the evan's against bc5. everything else is quite passive for black so you naturally have some initiative already in that case. you can't get similar options vs the spanish. i don't know much about the scotch though. the lines with nf6 can be quite sharp if you go nxc6 and e5, but black has other tries besides nf6.

You want aggressive and good or just aggressive. If just aggressive then Nc3, if black doesn't play Nf6 then just chill, but if black does play Nxe5. It's called Halloween Gambit, it work pretty well if the opponent haven't seen it before. If you want better and less aggressive then Scotch Gambit. If you want aggressive but still play normal chess then the Italian with potential Evan Gambit

I mean aggressive as in with most of what black responds with there will be an aggressive line. If move 3 is something that becomes aggressive only if "black plays x move", then I'm not really interested. I don't want to give black the option to steer it towards something "tame" (such as all the pieces get traded off, or there is no way to attack the king)

Here's some strong things as white: Center Attack, Fried Liver Attack, Scotch Gambit, Ruy Lopez

For Black: Giuoco Piano, Two Knights Defense, Blackburne Shilling Gambit

I play d4 so take my advice with a grain of salt

Scotch is pretty balanced and calm imo so not 3. d4

Ruy Lopez was a bit too maneuver-ish for me, there are a million different things that black can respond with etc

Italian objectively is probably the most "aggressive" given that the c4 bishop attacks the weak f7 pawn and there's going to be lots of pressure on Black's kingside, not to mention that you can always play 4. d4 and turn the game into a tactical warzone

The Scotch is most likely what you want.  You can get some sharp games without relying on a gambit. The Ruy Lopez is great, but not really what you are interested in.  The Italian is fine too but after Ng5 in the 2 knights, black is the one with aggressive intentions.  

Just pick one and go with it. From tournament experience, Ruy Lopez gives you strategically and tactically rich games. In terms of tactical channels, I have seen scotch gambit played a lot which starts with 3. d4. Bc4 is going to feel sharp when you get into some lines of the Giuco piano, but otherwise most people end up going for the giuoco pianissimo. TL; DR : 3.Bc4 - Mostly quiet, but can be tactical, 3 d4 - scotch gambit is considered aggressive, 3 Bb5 - unpredictable as the amount of positions that arise from this move vary a lot and depend on the player

I would also opt for the Scotch. In the Italian Black has some offbeat lines, which prevent the sharp lines (and the majority of Italian games are rather quiet) and in the Ruy Lopez Black can make the game a positional struggle (though chances for an active game are imo better than in the Italian). In the Scotch Black cannot really avoid 3. ... exd4 4. Nxd4 and you already have a battle in the center with minimal chances of making the position closed.

:scream

here is my opening vs the first grandmaster I ever played.

US OPEN CHICAGO  1973 ROUND 5

"After these moves, what third move for white leads to the most aggressive game? is it 3. Bb5, 3. Bc4, 3. d4, or is it something else?"
Kasparov had played aggresive games with all three.

I thought of Kasparov here too. Yes, 3 moves into the game hardly sets the pace...any of these three openings could potentially turn aggressive in nature of play.

Bc4 (the Italian) is very aggressive, especially if followed up with b4 against Bc5 (The Evans Gambit!) Scotch Gambit and Scotch Game are also quite aggressive and Bb5 (the Spanish) is a very positional opening

The Ponziani with 1. e4   e5  2. Nf3  Nc6   3. c3  can be a very aggressive opening if you know how to play it. I have beat strong masters with that opening.  However very few know how to play that opening.  Here is one of my games.

1-0

You can play Bc4 and if they respond with Nf6 go for the fried liver. If they respond with Bc5 you can play the Evans' gambit 4. b4.
Also, you can play the Scotch gambit
1. e4 e5
2. Nf3 Nc6
3. d4 exd4
4. Bc4

The Ruy Lopez may look slightly more passive, but white's attacking chances are hidden, waiting to be revealed. hehehe...

There is no opening that White can be single-minded and think that aggression wins.

You can not pre-meditate an aggressive game!  Not happening!  You force the issue, you lose!

Take the Ruy Lopez.  Black can take risks with lines like the schliemann.  Often this means White having to defend Black's unsound initiative, and if he defends successfully, he will likely have a winning endgame.

Black can play something like the Berlin Defense where breaking down his "wall" may require a lot of time/moves, and a strong positional understanding.

Then Black has passive lines where aggression is the answer.  These are where Black just tries to sit back solid, like the Steinitz Variation (3...d6).

The same can be said for the others.  There is nothing where White can play aggressively against all Black responses.

I agree with this. So what I'm really asking is if I were to play 100 games with 3. d4, 3. Bc4, and 3. Bb5 which one would give me the most games out of 100 that were aggressive? (or it could be some other move, such as 3. c3 that was mentioned)

You people don't think this line is aggressive?