This a question I am regularly asked and it really requires me asking several questions. Depending on the answers depends on what you need to get.
The first question is how will you use it. Will you just use it to do Internet and email and look at a few web pages? Will you be using it to do better photo editing such as Photoshop? Will you be using to play games?
The second question is do you want a portable device or a desktop? There are lots of options for both. If you want a portable device then you need to consider a laptop or tablet.
How much memory should you get? If it is just for email and internet then 1 gig of memory will suffice but more will work faster. If you were looking at playing games (then you already probably know what you need and would not ask) you need at least 8 gig of memory and really need 16 to 32 gig of memory. For game playing the more machine the better.
What speed processor should you get? I would suggest 2 gigahertz or faster for everyone. Just Internet and email could get by on a single core processor but at today’s prices I would suggest look at a dual core processor. A quad core or more cores would be good for heavier users.
How big of disk space? This will depend on what you will be storing. If you will be string lots of pictures or videos then I would get a terabyte or bigger drive. For those just doing basic usages I would suggest at least 250 gigabyte hard drive.
The brand will depend on your specific tastes and prices. Basically the internal components are all made by same companies. Some companies charge extra for their name. I have had success with Acer, store brand from Microcenter, HP and Dell, but that is a wide range of prices.
I would suggest Windows 10 for most people for the operating system. If you get Windows 8 try it first as many do not like it although it will upgrade to 10 free thru July.