It's a hard fact that All new Yahoo! mail sucks. This may be just personal but Yahoo gave me tough times with server errors on numerous occasions. For me GMail edges out Yahoo! Mail because of its speed and spam blocking. Yahoo! has too much spam, including IM span. Also POP access and disposable addresses require paid account. I'm afraid a day might come in the future when Yahoo won't allow access to your account even if you enter the correct ID and password. Once my Yahoo mail got hacked, I had enough with it. I was about to delete my account but suddenly I noticed that there were many important e-mails in my inbox! Now what?! Before I go into what to do next, let's see why GMail wins against Yahoo Mail.

Why to switch from Yahoo! Mail to GMail?

• Faster access to mails and general speed in sending & receiving mails. Powerful search function for e-mail similar to Google. Filtering out e-mails with .exe attachments possible.
• Better spam blocking and less spam. Yahoo has too much spam including IM spam. Yahoo! also sucks to differentiate b/w legitimate and spam mails.
• Automatic forwarding for GMail.
• Supported E-mail client access for GMail:POP3, IMAP, SSL/TLS supported, SMTP restricted. Yahoo supports only POP3 that too for certain regions. (This feature is to be noted as it's useful in the article)
• Gmail localization for 52 languages, Yahoo 27 languages
• GMail has text ads only in viewing mail box, not in messages. Yahoo has ads in interface and mails.
• Domain name customization possible in GMail using Google Apps
• Custom From address can be set up in GMail
• Address modifiers available in GMail (userid followed by + followed by tag)
• IE, Firefox, Chrome, Opera only compatible with new version of Yahoo Mail.
• Account expiration on inactivity 9 months in Gmail that too at Google's discretion vs 4 months for Yahoo Mail.
• Other special features in GMail: Messages grouped into conversations, Basic HTML view gives faster access for slower net connections, Labels are used in GMail instead of folders in Yahoo.

How to switch from Yahoo! mail to GMail?

1. Sign into your Yahoo account.
2. If you are using Yahoo Mail Classic switch to All new Yahoo mail. Click Options to the right of your mail box page and select All new Yahoo mail.
3. If you check Options(at top)->Mail Options->Forwarding, you can see that this feature is only available in Yahoo Mail Plus and you have to upgrade for $20. Oh come on, don't be sad. Read the rest.
4. Now go to your Yahoo inbox and select the display name on top left. It's your name written as Hi, "your name". Go to Account Info that appears in the subsequent drop down box under your display name. You may have to sign-in again to verify. 
5. In the Account Info page, scroll down and click on 'Set language, site, and time zone' under Account settings and set your Regional Site and language to Yahoo!United Kingdom and time zone as GMT UK. Now, save your settings.
6. Sign out of your account, close all browser windows and then sign back in. Click on "I accept the Terms and Service" pop up if it appears. If not, don't bother. 
7. Next go back to your main mail box page select Options from the top, go to Mail Options and select Forwarding from the left side bar. Surprise! You don't see the Upgrade to get this feature anymore! 
8. Click Access Yahoo! Mail via POP and select any of the options to download spam or not. That's all that you have to do in Yahoo.
9. Next log-in to your GMail account. If you are using Basic HTML version of GMail click on 'Switch to Standard View' at the top. 
10. Go to Options, which is the gear icon on top right and select Mail settings. In the Settings page click Accounts and Import tab. Now click on Import mail and contacts or Import from another address if you have already specified an account to import from, before.
11. In the wizard that appears type in your username, click continue and enter your password, click continue again. Select your import options and click Start Import. It may take a few hours or sometimes upto 2 days to start seeing your imported messages. Click Ok. 
12. You're done, within a few minutes or hours check your inbox or spam in GMail to see your mail and contacts that you've imported from Yahoo. If you wish to stop importing new messages click on Stop in the import mail and contacts page at GMail.
13. You may switch back your locale in Yahoo to your current locale, but I'm not sure whether your mails will be imported anymore. This option left to users.