Gmail provides POP3 access, Yahoo doesn't!! That's one important enough feature for me to stick to Gmail. With POP3, my hard disk capacity is my mailbox size
Additionally, Google Apps is pretty neat! Use Gmail features with your own domain! And that too for free!!
Yahoo may have 100 features. But IMHO, gmail still rules due to 10 features that it provides because of their usefulness.
And if space is criterion go to IndiaTimes (yucks!). They provide unlimited space
