Anandtech has several reviews of video/tv tuner cards posted over the last 18 months or so. Tom's Hardware did a recent comparison, check it too.
The whole question hinges on what features are most important to you, as they all perform a little differently. If your favorite games support Glide, then you probably want 3DFX, if it is hardware DVD decoding then it is probably ATI...Best 2D?(matrox has great 2D) Best TV picture? Video capture?
The question is really more complex than you might imagine, and only you know what features appeal to you the most.
Research is the consumer's most valuable tool.