I almost always play 1. ... d5, the Scandinavian or "Center Counter", in response to 1. e4, though I've yet to settle upon any consistent reply. for one thing, people react strangely to the Scandinavian, and are apt to play responses that aren't considered best play and yet which yield perfectly playable games, like 2. e5. check any book on the Scandinavian and they'll barely mention replies other than 2. e×d5, but I see 2. e5 frequently.
this opponent played 2. e×d5 to which I responded with 2. ... Nf6, the "Marshall Countergambit" variation to the Scandinavian. in practice it's difficult for the first player to retain the extra pawn. but then they played 3. Qf3 and eventually we ended up with this position...which they resigned. I feel a little bad about it.
~Azzy