Capping creates a perfect hermetic seal, while a wine cork "breathes" (that is it allows a microscopic amount of O2 through with reacts with the tannins in the wine to make it "softer" and more mature). If do not plan on aging your wine, then I can not see any technical reason why you would not go for a cap.
But forget all about that. Think of the presentation factor. You have your best girl on the couch, you have Barry White playing softly in the background while a fire is crackling in the fireplace. In a deep sultry voice you ask "would you like some wine my darling".
You then whip out a bottle opener and she see that the wine is in a used beer bottle.
Spontaneously, the fire goes out, the music stops, and (while she is on the way out the door) your best girl loudly laughs at how you need to open the wine with a church key. The next thing you know, she has broken up with you and is now dating a man named Dexter.
In short, I would miss that pop that announces "a good thing is about to come my way".