Budapest, Albin countergambit, or Benko gambit?

I want to study aggressive side lines to take the opponent off his repertoire.
I came across these three, but don't know which one to choose and don't know where to look for advice.
Any thoughts would be very helpful

Thanks!

Christof Sielecki (Chess Explained) has released lots of study materials about the Benko, including YouTube videos and a Chessable book.

I know Lawrence Trent recently released some study material about the Albin countergambit, apparently he came to the conclusion that it's quite playable.

Eric Rosen says he used to play the Budapest a lot, when he was rated higher than 2000 (presumably USCF rating) but before he became an IM. Perhaps you can ask him on a stream or just study his games somehow.

So all three are probably fine. Just pick one and have fun! If you really want to study the opening, then don't forget the opening book feature available here on lichess.

Budapest is very well known and some what weak but Benko is solid.

2/3 are rather positional lines resp. long-term compensation although they are dubbed ‚gambit‘. Starting with d4 and Nf3 I have nothing to fear. ;)

Indeed, the problem with Albin's Countergambit and Budapest Gambit is that it does not happen if white plays 2 Nf3. Benkö Gambit is the more solid of the three.

I would say you play budapest and try 4.g5 move if opponent plays Bf4 after Ng4

From the three options above I'm not recommending anything, although Benko is quite good.
The problem is that Budapest is not very good and Albin and Benko are more positional and long-term.
For your goal (study aggressive side lines to take the opponent off his repertoire) I would go for Leningrad Dutch with c6. (Played by Caruana, Nakamura, Svidler, Ivanchuk, Mamedyarov...)
(1. d4 f5 2. g3 Nf6 3. Bg2 g6 4. Nf3 Bg7 5. 0-0 0-0 6. c4 d6 7. Nc3 c6)
You can play this setup against 1. Nf3, 1. d4 and 1. c4. (but the move order can be tricky sometimes)
It leads to unbalanced positions and if White is not careful, Black has a strong attack.

For learning Budapest I recommend this free Chessable repertoire: www.chessable.com/trappy-repertoire-for-black-against-1e4-and-1d4/course/1570/

Just to point out this video of Eric Rosen giving a lecture at St Louis Chess Club: www.youtube.com/watch?v=2Sf3bDGm3wc

Budapest stuff begins around the 16 minute mark and continues up until about the 40 minute mark; but the whole lecture is fun and interesting.

Benko, Benko, Benko.