I would like to know which digital camera is best to buy of 6 megapixel.?

6MP is a nice start. That's plenty for full page prints.
In general, anything recent by the major brands will be good (Canon, Nikon, Olympus, Kodak, Panasonic, Sony). It's largely a matter of personal preference.
For specific recommendations, you'll have to provide more info:
What's your budget?
What kind of zoom-range are you looking for (3x, 10x, dSLR)?
Is low light photography important to you?
Should it be tiny or is a bulky camera okay?
Etc...
Here's a great site for in-depth reviews: http://www.steves-digicams.com/hardware_...
This site also has a lot of reviews, and some good user forums: http://www.dpreview.com/

Canon

Canon ixy

Once you get to 6meg cameras You have the best pictures. The problem is how fast does it take pictures & other things like that that should determine which camera to buy. If you are going for speed, pick one of the makers of 35mm cameras.

The Canon A700 is a good all around choice,6mp.,6x optical zoom,2.5"lcd,and an optical viewfinder (very important in bright sunlight) Also runs on AA batteries.