Gmail is the best one as per my view.
But if you really want alternative of Gmail then Go with hotmail.
1)Because they provide 25GB of online storage for all your data i.e skydrive.(including software,movie etc).
2)you can also use your hotmail id in microsoft login as well.
This all boils down to one thing .... How You Like to use your mail ID, How basically you would like to manage it.
For example , if you are sticky on using Mail Clients to get read and reply to mails then you need to choose you mail id with a provider that will give you every possible ways to use it on your Mail Clients.
From Folders sync support to calendar support etc ( to name a few )
Also many people use multiple computers and may like to have their mail come in automatically in each computer in a very organized manner.
Gmail does tops up the list for all this, since it still uses IMAP to sync.
So, WebDev and other POP may not be supported by your mail clients, so choosing the best ID for your particular use depends on yourself.
As far as the service quality provided by this FREE email providers are mostly similar and good.
Hotmail is very good since it integrates with MS Office ( read skydrive ) and also is now very fast to use.
If you like Gmail and want all of its features for your Yahoo Mails, Simply import Yahoo Mails in Gmail.
1. You get all your mails in Gmail
2. When you reply to any of the mails sent on yahoo ID , your Yahoo ID will be in the FROM section. Alternatively, you can also choose Gmail ID if you want. Its fully configurable.
Currently, I am using Gmail as primary ID and configured yahoo and my office mails in Gmail too..so i just have to login to Gmail and can read/reply to any mails from any ID.
Have you guys tried Microsoft's "www.outlook.com", I cannot comment on betterness, but Interface is really different unique and not very fancy. Someday when i will be free i will give my time to interact with this new email service. I liked the simplicity..check that out guys.