I'll give the answer I always give:
Nearly everyone selects computers in exactly the reverse way from the most logical. The most logical way is:
1) Determine what you want to do with the computer.
2) Determine what software is the best for doing what you need to do.
3) Buy the hardware that is best suited to run the software in the environment you need.
Now, compare that to the typical consumer's computer buying process:
A) Buy the hardware because it looks cool or seems like a good deal.
B) Buy the software because it looks cool or seems like a good deal.
C) Try to figure out what to do with the HW & SW you have purchased.
If, after completing steps 1 & 2, you learn that you really need a Mac desktop instead of a Windows laptop - then buy the Mac desktop - don't buy something that doesn't meet your needs. OTOH, if you learn that you can't afford the HW you need, then go back to step 1 and lower your requirements. Repeat until you reach your budget. That way, there will be no surprises when the HW you buy can't actually do what you want it to do. Don't forget to include environmental requirements as well as technical - will you be traveling with the computer? Will you need the internet while traveling? Is weight important to you? Battery life? Screen size? What kind of things will you be connecting to the computer? How many at the same time?
The more questions you ask yourself, the narrower the choices will become - and therefore the easier it will be to decide. Good luck!
BTW, I'll give you a recent example of how not to do it...
A guy that travels all the time asks for as light a laptop as he can get - but it still has to be very fast and have a super sharp screen. He selects a Samsung Ultrabook. It is a really sexy machine - I7 processor, beautiful 1080p screen and super thin & light. After he gets it, it is everything he hoped for!
On his first business trip he discovers two things:
1) There is no DVD drive. He likes to stop at Redbox on his way out of town and pick-up a few movies to watch on the plane. Now he either has to rip the movies to his hard drive before he leaves, or he goes without movies for the trip. When he does try ripping a bunch of movies to the hard drive, he finds that the movies plus his itunes music library, plus his huge offline mail archive have eaten up most of the space on his blazingly fast 128 GB SSD drive.
2) When he arrives at his first customer meeting and attempts to hook-up to the conference room projector, he discovers that his new laptop does NOT have a VGA port. It has only a micro HDMI port, and the customer's older projector has only a VGA port. The meeting is a disaster because the customer has to scramble to get their own laptop, transfer the presentation to the other laptop and then do the presentation from there.
So - the guy has to make some changes. He now carries an external USB DVD drive. And he also carries a dongle adapter that converts micro-HDMI to VGA. Finally, he also carries a small 1 TB USB hard drive that holds his old mail archives and his music library.
The result? He is now carrying a total weight that is *more* than a traditional laptop that would have a DVD drive, more storage and a VGA port!!
That's a true story...