Mac. the one thing I like about macs in general is that they run virtually silently. My PC sounds like a beast with its crazy fans and stuff. Newer PC's are probably better now, but nothing is quite as silent or sexy as a Mac.
though I do have a P4 with Windows and Linux (screw dualbooting, I have a removable hard drive bay with two hard drives 
)
I also have a PowerbookG4 which has served me well. I love expose!
My next purchase will be a mac mini when Starcraft2 comes out.
I know at least 2 staunch MS people who are at least investigating Linux. I had been arguing with them for years now about how much Windows is teh suck. Now I have to face the task of not rubbing it in
As for documents and spreadsheets, i prefer Microsoft Office 2000 or so. Anything newer than that has too much eye candy and the extra buttons and characters and crap just annoy me now. You have no idea how much I've wanted to kill that stupid talking paperclip!
But when prices becomes the issue, $0 for Openoffice which does everything MS does (plus publish to PDF) is a way better value to me than $150 for a legit copy of Office. Students can get the student version I think for about $50, but in reality most everyone just downloads MS Office off the net or pirates it from a friend.
