I'm going to toss my vote in for PC. I have used mac and PC both equally and extensively. Going foward you will have more options by sticking with PC as you can use mp3's more trouble free and transfer songs to other devices easier because with Apple, once you start usin their stuff you kind of have to stick with it for life or else you mind find their library system and aac files give you hassles on non Apple stuff.
A PC with a decent soundcard (m-audio) will provide great flexibility.
A PC with a decent soundcard (m-audio) will provide great flexibility.