If you work with graphics or do photo editing, you'll want the larger sizes. The more RAM a card has, the faster it can process and display information, as well as produce higher resolutions. Here, 4MB is the minimum. If you don't do much with graphics or games, it will be sufficient. Otherwise, make sure your sound card uses Wavetable technology rather than FM Synthesis.
Wavetable technology produces a clearer, more lifelike sound.
Some of the better cards simulate 3-D surround sound. No matter how good your sound card is, the quality of the sound will be determined in large part by the quality of the speakers. Speakers that include a subwoofer will be able to greatly enhance the deep bass sounds. A little extra money usually goes a long way in getting better quality sound from PC speakers. They are measured in spin rates with higher numbers being faster.