What is better to purchase desktop or mobile computers?

Hello jt327-ga, 

Neither is inherently better, it depends on several factors. You need
to evaluate your needs and make a decision at that point.

Some Main Benefits of laptops over desktops:
-less space needed
-mobility (although this depends on what notebook you buy, some are
too heavy to carry around)
-compact form factor

Some Main Benefits of desktops over laptops:
-cheaper for the same power (you pay more for the small components in a laptop)
-easier to upgrade
-you aren't stuck with the same screen size for the life of the unit
(although an external screen can usually be plugged in)

Here are some good articles for further reading that I recommend: 
http://hffo.cuna.org/story.html?doc_id=1122&sub_id=12433
http://www.microsoft.com/athome/moredone/lapvsdesk.mspx
http://reviews-zdnet.com.com/4520-7298_16-5121574.html

Good luck choosing! Let me know if you need any clarification,

tisme-ga

You can use your laptop laying bed; perhaps very important for some
disabbled persons.  Neil

My perception is that Desktops are more reliable than Notebooks.

in particular, batteries can be a problem!

Note Dell's recent recall of a mountain of batteries.

Thunderstorms can zap your desktop too.  

With the advent of built-in wi-fi the laptop is my first choice.  I
use an old desktop at home and a KVM switch when I want to use the big
screen and keyboard with my laptop.