TIP: A tablet, netbook, or laptop computer gives you flexibility.
Whatever computer you purchase, I recommend getting a laptop (or tablet or notebook or netbook) model. The compactness gives you the flexibility to travel not just around town and the world, but around your home and yard. A small computer takes up much less space and is far easier to move than a huge monitor and computer unit. You might pay more for a smaller computer, but buying a used computer that is one or two years old, you can get a very capable machine for little money. I prefer owning the smallest and simplest possible computer for my needs.
A small computer can allow you to travel about and have Internet access and your files. My own netbook (an EEEPC) is still in use; see My Computer Notebook.