Thats an interesting way to say it, anyways, I would suppose video. Although, getting a sound card (and assuming you have a video card) can reduce FPS in games, so that could be argued that, the sound takes more resource too use.
Pretty close in comparason. But if you were looking to get a sound card, or a video card, I can defintly say the video card, unless of course you dont play games, or dont have 5.1 and you have a 5.1 sourd setpu.