Can you tell me what is the best CMS and why it is important?
If i have a E-Commerce site then what CMS would be batter for me?
What research have you done so far? You are asking a lot of very generic questions, for which there are already thousands of answers online.
Look i asked because i don’t know the answer?
Sure, but it’s best to do some research first. For example, if you google something like “which is the best ecommerce cms” you find that there are lots of useful answers already.
A better use of a forum is to ask about a specific problem you are having. It’s not about getting others to do your homework for you. 
i asked here because those answer’s was not so much perfect? but i can understand your point of view. i will try to follow your rule. please don’t banned me.
OK, that’s fair enough. I don’t want to be mean, but you have asked a lot of questions that are easy enough to research. Perhaps tell us about what you’ve read so far, and ask some questions about that. Did any CMSes look like they might be right for you? Did you have any questions about a particular CMS?
Or another approach is to tell us what you need your site to do. Can you list the features you need? That’s much more helpful that just asking “what’s the best” anything. “Best” means different things to different people, depending on your situation.
Yeah, the reason most people won’t answer this question is because it’s been done to death and usually attracts a scourge of “pick my favorite CMS” responses without backing them up with any facts. This site alone is certainly full of examples of that if you search “best CMS”.
Back to your question…
You will find that pretty much all of the popular CMS packages support eCommerce in one way or another but as ralph.m said, we’ll need some specifics in order to point you in the right direction.
How involved will you be with the design, development, administration and maintenance of the site? Where will it be hosted (shared server, VPS, managed server)? How much traffic. How many products? Who are the audience and is this big/small budget stuff?
Armed with some of that info, I think you might get some useful responses.
Cheers,
Andrew
i think joomla is still the best CMS,
but very hard for operation, espesially beginner in web desainer.
but, best a cms depending on the intended use