I use yahoo for my personal account and gmail for my school account. Gmail is much, much better. Also, if you go with yahoo and you want to use it on your Android phone, you have to download the official yahoo app, otherwise the generic email app won't let you send or receive emails to/from your yahoo account while on a wifi network. While it's probably trivial to get the yahoo app if you don't have a 4 year old Android like myself, if you don't have it then your email service will be next to useless on your phone if you spend a lot of time at home or on a public wifi network. Absolutely useless.
Plus, even with the yahoo app I always had issues with sending and receiving stuff - it just wouldn't work half the time.
So go with gmail.
I also receive much less spam on my gmail account and it's easier to set up filters for stuff (like spam - or to automatically shunt certain emails to certain folders to keep your inbox clean) than it is on yahoo.