I'd start with an Intel i3 or i5. At those lower end cpu's I've heard those are the better choices. A laptop might be handy -- depends on what you are doing. But you can take it from the shop, to breakfast table, to bathroom if you need. An i3 will run sketchup, do email, run Excel, and browse the net ( I use Chrome). I don't like win8 -- hate it in fact. But if you get it, and don't like the wizbang user interface, you can download 'classic shell' and get your start menu back. I say this because you may find that win8 comes installed and you have no choice. I don't think one brand has a big advantage over another. I have heard good things about Asus. I bought my daughter a HP, which seems decent. I have a Toshiba and older Lenovo. My son has an Acer. The old Lenova has the best keyboard -- but the newer ones are probably not as good. We test drove an Asus. I liked the keyboard, but the HP had the i3 for just a bit more $. The HP's keyboard is better than the Acer.
I'd probably look for best price on an i3 or i5. Then shoot for the Asus, HP, Dell, Lenovo, and last Acer. Our i3 HP was $380 I think. 4GB RAM, 500 GB disk. I'd buy a cheap external disk also -- and then backup the important stuff. Try to get one that has space for 8GB RAM if possible. But that depends... I figure the i3 will last us at minimum 3 years -- more likely 5 -- and possibly 7.
If you are going to get a desktop -- those can be pretty cheap also. And you already have the keyboard, mouse, and display (or will have). Then you can just focus on the CPU really. The laptops are handy.. but more flimsy.. so if you are hard on things, consider that.
I look for where there is a big price drop-off. Right now that seems to be the i3 or i5. You go above that you and you are paying for the privilege to own newer technology. I let those who need it pay for it, and I take the sweepings that give me all I need at sub $500 prices. My 2 cents.
PS -- but I don't use Autocad. And I don't do anything graphics intense. I find sketchup is all I need -- and more -- and runs fast on the i3, or in fact, older CPUs.
