I've had Yahoo, Gmail, Skynet, and Hotmail. Gmail is the only reliable one in my experience. Yahoo is a hotbed for general spam. Hotmail - Microsoft, rather - spams me with its own "buy these products!! " mails. I forget what skynet does. Gmail is just right.
I use both Yahoo and AOL as providers for my e-mail accounts. Initially I used AOL for my very first e-mail account, of which I quickly lost interest in. Then I made my second e-mail account, one of which I use much more frequently, on Yahoo. E-mailing, and e-mails in general, are not very important to me, so which website I use doesn't necessarily concern me.
I use Hotmail and AOL for informal staaf, and Opera Mail for proper things, I use Opera as a browser so it's really easy and simples I don't know how safe it is, but it hasn't failed me so far *touch wood*.
I use both Yahoo and Gmail, but I'm starting to use Gmail more, since my Yahoo is overflowing with spam. I never really send out emails either, but just use them to sign up for various websites and programs.
I have many email accounts for various sections of the net. I have the following, Gmail, Yahoo mail, Hotmail, zoho mail, mail.com mail, the worse mail I've ever used is Hotmail however, so many spam bots on that network it was unbelievable, any account would essentially get 100 or so spam in a matter of days in dual time. I'm not sure how it is now though as I've migrated elsewhere for main use mail.
Because I hate yahoo's interface. I can't use it. My flood of college emails get sent there as does my junk. My real email is gmail. It has a good clean interface and nice background chices. I have one at live.com since I had to with win 8 but its not used.
Edit: Also ads. Yahoo, the login page is an ad. all of it. Google I rarely even notice the ads.
Gmail has a really nice interface, and I noticed that they updated it again very recently. Personally, I prefer my own server since I can set it up exactly how I like, but as far as the typical e-mail providers go, I think Gmail has been pretty great... well, up until they began tying user accounts into every other service they own.