This is a tough question and its hard not to be biased because I have accounts with all three of them, and each associated with have there very own benifits.
First off Gmail is by invitation only, it the better user interface, more file storage, and larger attachment files then Hotmail or Yahoo truly. In this manner if you are looking for a proffessional and powerful email service then Gmail is your best option.
Second is Hotmail, hotmail is free but there cp is not that friendly, they have kept the same old look since the beginning, you cannot send very large file attachments, Locate that you get much more spam with hotmail, if however you use MSN messenger for personal use then hotmail should be the selection of an email service because you dont need to use your email address for anything else, maintain it as a dummy address, empty the actual spam every once and awhile, and use it to talk to people you dont know personally this way you dont wreck a good email.
And last while least is Yahoo, well I put Yahoo in the heart of the two (Gmail Being The Best), Yahoo does possess a friendly user interface, and they carefully consider a moderate file attachment size, there POP access is super easy to set up, and they offer more things then plain old gmail. Yahoo is an excellent personaly consider anyone who does not usually do lots of things online.
So it really depends on may well be a the E-Mail be the cause of. If you need it for MSN and some chat sites go with a dummy Hotmail account to avoid spamming your good accounts. If it ought to be for a basic everyday personal use where you will not be requiring a great deal of traffic then opt for Yahoo. But undoubtedly if you need your email to handle traffic, offer a great user interface, obtain the proffessional look, and be able to send larger files (The more interactive online user) then Gmail is the e-mail of choice for.