Personally I find the build quality of cheap PCs are terrible, I have seen so many cracked cases. So I would not go for one personally. My wife has a 2006 Macbook that has only just been replaced, she used it every day and it has been a great machine (though the battery has just died this year) I think this is a testament to quality. It has just been replaced by the new MBP retina – sweet.
Myself, I have a work HP Elitebook, awesome windows machine but you are talking mac money, but it is the only machine I can honestly say is of Mac quality. My home machine is a Dell XPS15 – which I replaced a macbook pro with, I was a sucker for spec and wanted quad core, nice screen etc (pre quad MBP) and I really wish I just got a macbook, as nice and expensive the Dell is (£900 machine) – its still not got that quality feeling but it is fast.
So personally, I could only suggest getting a mac, the quality is amazing and I think that ensures longevity. And remember they all run windows really quite well (Arguably better then they run OSX – I got geeky once and wrote an article on this and benchmarked a bunch of intensive application on a few separate macs running windows and OSX and windows was ALWAYS faster).
Get a mac and run the OS you like.