If you are thinking of upgrading your present desktop computer, obviously laptop computers are the most possible variant you will be looking for. They are slim, small, compared to desks and most importantly - portable. However, there are some things to consider when buying a laptop computer:
1. Price.
Laptop computers are a bit more expensive than desks, although you do not have to buy monitor as laptop combines both. In this case the price is somewhat equal.
However, I suggest assessing your needs considering the size, performance qualities, brand and guarantee service.
2. Size and performance.
Even laptops are of different screen size and thickness. The smallest laptop has a screen of only 10 inches, the largest screen sizes can reach up to 19 inches and more. If you are going to use it mostly while traveling and only for checking email, browsing the internet, creating and editing some office documents or watching a movie occasionally - then netbook computer will definitely fit you. They are small, light, and not too expensive, plus, some brands have long lasting battery life, for instance Asus EEE PC 1008 HA. They can not boast of superb performance qualities and I doubt, if you will be able to do some graphics works with the mini laptop computers.
On the other hand, if you will be working at home, making and editing files which require much memory, playing up-to-date games with good graphics card along with powerful multiple core processor - then 17 or 15 inch laptop with some Intel dual or even quad core and at least 4 gigabytes of memory will suit you. They are more expensive than small laptops, but the difference between working with a 10 inch screen and a 15 inch screen laptop is obvious - you will not be able to do much graphics with the first.
3. Brand and guarantee.
I have my own opinion based on my experience considering the brands choice. I would personally choose Dell, Asus or Lenovo, and would be cautious about HP, Acer or Toshiba. I have worked with Dell computers a lot, including desks, and even a 10 year model would run like a clock, not mentioning the brand new laptops. I am currently working with Dell Inspiron 6400. Three years have passed and I still have no trouble with it, even system software has not been installed, because there is no need to. Beside, the guarantee is 3 years (at least in my country, it might be different in other countries). Another option which I would consider is Asus. Asus producers have the best statistics of small break number in the first three months of purchase. Their breakdown number increases in the longer term, but the statistical figures are still impressive.
Lenovo brand is known to be former IBM - which has always been a quality trademark. Lenovo laptops are not cheap, but they are worth it, although the guarantee is only 1 year.
HP has had some serious problems with HP Pavilion series, when a vast number of models broke down because of faulty graphics card chip. The funny thing was that many models broke down after approximately 1 year of purchase, and most of users could not use guarantee service, which is only 1 year. The problem was simple - the chip had no decent radiator to dissipate the heat and the connectors bounced off the motherboard due to extreme heating. You could bring the model to computer repair shop, change the motherboard with another video card or buy another computer. All the variants were pretty expensive. I would be more careful choosing the Toshiba or Acer model - they tend to collect much dust in a small fan area and start restarting due to excessive heat. I hope, producers have deal with that problem in new models, and then it's another story.
I would also pay attention to guarantee quality service. Where it is located, what's included in the repair works and what's not - those are important points, once you start experiencing some hardware problems.
Having said all the above, try to define your needs, the price that you are willing to spend and the brand that you know most of.