Dont forget to add a warranty+repair service as a positive for prebuilt and a con for self assembled. The warranty service that comes with literaly any prebuilt computer that is not really possible for self assembled computers has saved me several times.
Just phone the company, spend about half an hour on the phone and get a free computer repair as long as you arent an idiot that spills apple juice on his laptop.
Make some attempt to be less biased.
Also, I am looking to get a new hard drive.
I just upgraded my motherboard to use the new fancy 6gb sata things but my hard drive apparantly sucks. I was looking online and I found something called Buffer Memory.
How important is it and what should I get if I have a hard drive budget of max $50?
Edit: Looking through your hard drive choices, they all are poop.
No 6gb/s
Overpriced for amount of disk space
Inferior buffer something (whatever it is)
I would replace literally all of them with this:
http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=744451&CatId=2459