The integrated Intel GPU is not bad these days, and can handle normal videos quite well, but if you are going to do any serious graphics work, then the Radeon is a good choice. If mostly you are going to do software development, then either will do you well, unless of course you are interested in GPU programming.
As for OS, my preference is to run Linux as the base OS, and then run Windows in a virtual machine under Linux. I user VirtualBox as a virtual machine manager - open source, free, and very reliable. The ability to snapshot your virtual machine means that if your Windows VM gets a virus, you can instantly fix it by reverting to the last snapshot. Ipso-presto! No more virus! I do both Linux and Windows C, C++, and Java programming, mostly cross-platform stuff that has to run on both Linux and Windows. This setup works well for me.
Screens. Well, I have a Lenovo at work w/ 17" HD display. I still use an external 24" display for daily work. My other laptop is a Dell D630 w/ 15" display, which is ok for travel, but I have it connected to ... a 24" external monitor when I am working at home on it, unless I happen to be sitting in my living room easy chair with it in my lap. So, save the money on the screen and get a good external monitor that gives you better resolution and bigger display.
Warranty? I prefer 3 years. My experience is that everything that is going to break does so either right away, or somewhere around 1.5 to 2 years. I've had drives, motherboards, and other cruft break (overheating problems mostly) around the 2 year mark on just about every laptop I've had. Why do you think all these manufacturers are going to 1 year standard warranties? Dell used to give a 3 year one on their business systems (Latitude), but have recently ratcheted that back to 1 year standard. Now you have to pay for the extra years, but it's worth it. A drive will set you back about $100, and a motherboard a lot more than that!
Anyway, back to screen: a high-res 14" screen is preferable to a lower-res 15" one. The more pixels the better, IMO. That way, you can increase the font size easily enough and still have crisp images.