d4
So, just check out these and settle on what suits your needs, but if you just want the most aggressive option, go for the Albin, the Leningrad Dutch or the King's Indian.
These answers to d4 are for relatively experienced players. If you're not too experienced go for the black side of the Queens Gambit Declined. Much more straightforward for newer players to the game.
I think newer players should take risks.
Edit: My suggestion, the shara henning, is out of place. I did not see the actual rating of the OP. It is far too advanced, @Karpak's suggestion is completely on point.
I think newer players should take risks.
And I think newer players should understand what they play.
Actually they take the risk of blundering badly right from the start of the game- they don't need more risks.
I thought he was 1400 (when I moved the pointer over the name it showed 1400). I did not know he was only 900+ (most reliable rating atm). In that case the gambit I suggested is too advanced, he should be playing relatively simple and straigtforward stuff, like the QGD (as mentioned by Karpark).
I'm pretty sure you'll see at top level the majority play d5 and nf6, they are both completely fine, although I prefer nf6. D5 is a bit more simple than the other choices (Nimzo Indian, Grunfeld, Benko, etc), so I'd recommend that to you.
Uh better put, QGD and Nimzo Indian are seen around top level more, I'm not exactly sure about Grunfeld and Benko but I'm sure they're fine
Grunfeld is very popular at top level. Benko less so.
There are lots of gambits you can try, Benko has one of the best reputations for black though. Also there are some more gambits associated with the Benoni and off course there is the Budapest Gambit.
But with rating below 1000, it isn't the opening you need to worry about but playing consistently well, without blunders and with aggression, developing pieces, controlling the centre and stopping your opponents plans is more important.
If you want to have a fighting game I recommend the Dutch against d4 :)