1.
I would suggest a laptop anytime for the main reasons:
-Mobility
-No noise
Secondary reasons:
-Lower Consumption
-Fewer Space
Laptop Drawbacks:
-Weaker
-More expensive
-Vulnerable
-Less upgrade options
If you get a laptop, I would also suggest to get an extra keyboard, mouse and screen and use your laptop as a Laptop-Desktop.
2.
Then you have to decide why you need the pc. If internet is the main thing, pick a cheap one with at least 2GB ram and a 2GhZ processor (Comparison list about processors: http://www.notebookcheck.net/Mobile-Pro ... 436.0.html ). A hard disk of 250GB at least and a screen size of 15"4 (if laptop) and 19" for desktor/laptop-desktop.
Bigger inch screens tend to be non-productive and tiresome but are good for movies/gaming.
If you need it for games, you just need a good graphic cards. ATI is doing great lately, especially for laptops. Use this site for graphic cards comparison: http://www.notebookcheck.net/Mobile-Gra ... 844.0.html )
Monstrous graphic cards should be avoided unless you are doing much video processing and/or 3d rendering in your work.
3.
Brand
Brands mostly matter when you are a newbie in regards with pc's and require support. Brands also matter a bit in laptops quality. Some are better than others. Especially pay attention to case materials if you are buying a laptop and you intend to move a lot.
4.
Protection for new pc:
Antivirus: Avast Free Edition
Malware protection: Windows Essential covers you.
Final verdict:
Investing big amounts in getting monstrous pc at the peak of technology should be avoided. It is more cost effective to buy a cheap one and get a new cheap one after about 3 years. You will also find that the actual life of your pc can be longer if you do not have high demands.
Extra:
If you bought a good pc 3 years ago, you most probably won't see much differences if you get a new one. So you could better invest in a SSD drive which will get you better results in lower cost. You can even keep the SSD for the new pc you just postponed and will ultimately buy
