I think an Einstein-Rosen Bridge, if we ever find one. Problem being the existing ones will already go to a specific place. Should we survive to a Type II civilization, we may be able to create some to specific places.
I also think "warp drive" is a high contender. This is what I briedly explained earlier, you "warp" space time around the ship to travel. Theoretically there shouldn't be any problems with it. But we don't have the technology to contain the amount of energy required. Eric Davis has written some great papers on this.
Another intriguing one is what sci-fi would call "hyper space". Basically another dimension that you slip into that you can travel in and jump back into our dimension. This is much more theoretical and there is a lot of theory but not a ton of evidence this would be possible. I personally believe that a Type III civilization had mastered all dimensions and uses hyperspace as it's main form of travel. Be we are very, very far away from that.
