Last couple of hours I found one different in gmail and yahoo mail.when you use yahoo mail so you can store your mail in particular folder which is create by you.but not facility in gmail..
I have been using Gmail with Mozilla thunderbird for quite some time and really like it. Yahoo doesn't allow any mail clients.
Gmail is significantly better, it's "spam" filter is far superior. Not only that gmail offers more features than yahoo, such as inbrowser chats, custom backrounds, etc.
I find GMail much better, because it doesn't have the ads at the bottom of the email, and I can easily integrate it with any domain I own via Google Apps.