i use the booth output on my djm, that way you can adjust the recording level of the mix, ideally you should be using the rca to 3.5 jack from the mixer into a line in on the soundcard but some people like myself dont have one so the mic port has to do, i use soundforge to record mine, its really easy to use
ps. just make sure you have the levels set correct or your mix will sound either too low or too loud which will make the bass sound distorted, i recorded that latest mix of mine slightly to loud, you can hear during some mixes when the 2 are playing it distorts slightly, ill fix that for the next one