If you're planning to get an iPad 2, and would prefer to have better audio capture capability, the Wi-Fi model might be the one for you.
According to iLounge, the difference in audio capture capability of the Wi-Fi and 3G models might be due to the difference of microphone location. The Wi-Fi models have the mic hole on the metal housing of the iPad, while the 3G models have the mic hole on the plastic antenna strip.
So, if audio capture is important to you, you probably should consider the Wi-Fi model.
iLounge article on iPad mic differences [article link]