I want to start web-designing website. Can you tell me which cms is best to start web designing website?
Can you supply a little more info? Do you mean you want to start a website that advertises your interest in designing sites for others? And you want a CMS for _that_ website? Or do you mean you want an existing CMS that you'll use as the basis for each website you design for others? Or ... ?
They are all good... Each site you design should be based on its own merits and thus a site build for Joomla, might not work for Wordpress and vice versa!
for simple portfolio website I recommend Wordpress. but if you need more complex one go for Drupal. I'm not recommending joomla
The nesessary question is... Do U intend to write about general webdesign, or about a special cms (the one U use in the site)? oscms TopHits http://www.opensourcecms.com/index.php?option=com_content&task=view&id=401&Itemid=184 There R some cms that is very difficult or even "backwords" to make custom layouts with. Unfortunately I have only tried a few and so far I did not like what I found. All CMS's tend to be at an IBM-DOS kind'a level if compared to modern Draw applications.
I'd recommend MODx as a CMS you only need a few hours of familiarisation to achieve something good. It's an awesome CMS and very quick on its feet. It's got MaxiGallery for holding images. Wordpress is a simpler but ease to use CMS. It's not really designed as CMS so it's more difficult to do some more complex things.